Let us boil this down to the root question "Do watts matter?"
Years ago, I learned electronics as a career gig before audio became a hobby. Makes sense, when in school a boombox fit my needs at the time so press on. Since I had the supernatural ability to install a car stereo by making my own wiring harness, installing the speakers and doing the proper tuning without burning up the electrical supply I became "that guy". I learned quickly when people wanted "help" it means YOU get stuck doing the full installation and I don't find being upside down in a hot car sweating while wiring to be particularly enjoyable so rapidly became an "advisor" not an installer! The sub amp think was the dominant question with an almost religious ferver when it came down to diameter of the subwoofer, brands, how it was loaded and more power was always the answer! I specified low power at the start because I did not want to purchase a high amp alternator, batteries used in commercial trucks or use electrical wiring the size of my thumb. It was a 100% stealth install to include the stock faceplate (mounted with magnets) to cover the CD deck and the subwoofer was built and installed in a gym bag complete with socks hanging out. The sub was a ported 10 inch subwoofer tuned to around 30 Hz, high passed at 25 Hz and used quasi-metric EQ to smooth down the mess. The speakers I used were very efficient at around 93dB 1w/1m and the sub had the maximum effciency I could get in that sized enclosure. It had the capability to get your ears ringing and over 120dB of bass response so I was content. The fun part was I never told them what amplifier power, speaker brands or even where the sub was located. The way to avoid those mall parking lot testosterone battles was call it a "SQ" (sound quality) system
A co-worker wanted the sound quality I had but more...as in MOAR! He had a pile of car audio magazines (early 90's) and not only drank the Kool-Aid..he was drunk on it. Attempting to teach him about watts, speaker efficiency, inverse square law, proper wire guages, alternators, batteries and so on would of been a waste of my time. By then I realized that I could not teach the world and have a life at the same time. What I did was take a pair of PA speakers (6 to 8 ohms impedance 100dB at 2.83V) and a car amp that produced 15 watts per channel into 4 ohms or around 10 watts per channel into the 6 ohm PA speaker woofer impedance. I told him the rather small amp was a Class D that pushed big watts per channel
and he fell for it. Sure, I wired it into the 20 amp fuse on his panel but...reality does not matter. He took his hatchback out, the high frequency and midrange horns pointing directly at his ears for a bit of blasting. A few hours later he comes back with a big smile on his face complete with his ears ringing. After all, if your ears are ringing that is the built in physical max so...
I broke it to him that the amp produced about 10 watts per channel and what he was hearing was massively efficient PA speakers with bass response boosted by cabin gain. It is almost impossible to go into denial when your ears are ringing! Welcome to 18's class called "Watts don't matter" and he learned about speaker efficiency, speaker power handling, converting watts to amp gain or dB/W, the inverse square law, basic horn/waveguide theory, dispersion and speaker bandwidth with the focus on subwoofers. In mall parking lot audio wars, always use a thousand watt amplifier (into 1 ohm) and drive it at 2 ohms or even 4 ohms to get 250 to 500 watts to prevent frying your battery/alternator but still have mall street cred by having a "thousand watt amp"
Going with higher efficiency subs (12/15/18, ported/bandpass) will give you the insane SPL without blowing up the electrical power or dim your headlights like noob systems. It "is" a thousand watt amp technically--learn to lie legally!
Watts are just one tool in the tool box of audio, by itself it is meaningless. Speaker efficiency, speaker power handling, speaker impedance, listening distance, how large is the acoustic space and even room reflectivity all play a critical part. My buddy wanted to have a party in the woods--he had the two greatest audio enhancements ready ever devised. Basically, alcohol and women in shorts--those two things always improve sound quality. We used my 4 ohm load 157 pound each 3-way PA speakers and he drove them with the rear two channels of his 4x75 watt car amp. Rotated the balance to the rear channels and hooked them up. Those 4 ohm monsters produced 103dB one watt/one meter so at say 63 watts with the engine off, that calculates to 18dB of amp gain. 103 + 18 = 121dB each which was deemed reasonable SPL for a party in the woods. Figure around 110dB peaks at a distance of 10 feet so it was time to party! We had a good time for around 5 or 6 hours, crashed to our tents once the keg ran out and all was well. Generally speaking, the speakers were not driven into clipping and the load was low enough not to kill his monster battery so we could drive out in the morning.
Obviously, if I had two completely different sets of PA speakers I was either the villiage idiot or used them for PA purposes--a little of both actually! Doing PA systems brings you to the real world quickly, you have to learn what "loud" is in decibels, you learn that wall outlets have a limited amount of power to feel power hungry AB amps, more power applied means more distortion as SPL has an inverse relationship with sound quality. Other things like dispersion become critical, room acoustics will bite your butt if you can't predict them or have ways to minimize their effects. After all, you are the "professional" that should be able to fix the acoustics in a school gym to get stellar sound quality--right?
Yeah, but the advertisements say that the Spazmaster 3000 will cure all acoustic ills with a push of the button! The best thing I ever purchased in pro sound equipment was a book--because throwing money at the problem is an option but knowing I'd have to carry all those racks up a flight of stairs created the weight limit rapidly. Time is not unlimited because I had a day job so learning about acoustics, EQ, PEQ, delay etc. and taking measurements saved a ton of time when doing proper setup. Times up and the show must go on. It did not matter what I thought of the sound, it mattered what the people that paid money at the door thought of the sound. If you consistently do it wrong, you won't get hired and will take a bath on resale value so education was not optional. Nothing personal, just business. I did PA for 9 years--good times but once you hit 30 in the nightclub world--you are old and a bit creepy... that was fine, I learned what I needed to know so sold off most my gear and pressed on. One pair of the small PA speakers became my garage speakers so I didn't need rockstar mode in the house. After a few brews, it sounded good and only got better the longer the night wore on (or until you fell asleep, cops show up etc.)
Consumer audio in your house has the same rules that apply be it car audio, PA systems in rooms, party systems in the woods or computer speakers. The room acoustics is the variable as it changes depending on room size, reflectivity or if no room at all. Car audio is nearfield to the extreme, PA systems outside in the woods is farfield in the extreme but the rules for amplifier power don't change. Room acoustics, speaker positioning etc. get very complex quickly or why there are engineers that study that science. However, amplifiers and their interaction with speakers are not a complex subject. Sure, you have power compression, beaming, lobing, distortion etc. with speakers but amplifier power is rather simple. Basically, understand the relationship with watts to amplifier gain in decibels, learn the rate of speaker SPL decline over distance, understand the difference between efficiency and sensitivity and how to calculate it. If you like, get a SPL app for your phone and measure the decline in SPL difference between 1 meter (39.4 inches) and the listening position where your head holes are located. Once you get that measurement, say it is -8dB in YOUR room...now you can calculate SPL accurately with amplifier power as long as you know actual measured (third party) efficiency measurements of your speaker. If you want 100dB peaks rated C in dB you will know 108dB is required from your speakers at one meter. That can be easily calculated by converting watts to dB of gain. Don't be a moron! Learn the difference between A weighting and C weighting with SPL meters--don't want to look like a fool and go safety nanny screaming about how 85dB rated C measurements can damage your hearing when that is actual A weighting in measurement. Learn what C weighting is and how it drastically differs from A weighting. If you care about hearing damage, always use A weighting because C weighting is used for frequency accuracy testing--not hearing damage. It matters!
In summation, watts only matter until they don't matter. The area they don't matter is when other factors matter more be it room acoustics, speaker efficiency, distance from the speakers and so on. My system will hit reference levels at less than 40 watts to any speaker in the system (measured) My AVR has the limiter set at "0dB" so keep spinning that knob, it just stops. Would I get better sound with outboard amps? I have two outboard amps and I did screw around with them cuz...beefy amps are cool.
My beefy amps are generally used for my PA system out in the garage but I bring them in during the winter and want to play with my toys. Alas, they also have power/clip lights and if I really care, I can plug in my laptop to the USB outputs and get actual waveforms and readings in real time. Nothing cooler than that... gangster audio points. My AVR still kills the party at less than 40 watts for the mains but my subs can easily drain over 1,000 watts during movie chaos so I feel better. I did this specifically by design. My living room MLP is 11 feet but I might move and throw the system in a full basement with two rows of seats! My mains can easily handle 250 watts each (tested) so I would get and outboard amp for my left/center/right because I have two rows of seats. For living room use I don't need outboard amps but for full basement use with two rows I will. The system design is flexible enough to add more power when needed, not needed now but that might change in the future and I don't want to throw it all away and start over.
The last piece of advice applies if you have pre-amp outs on your AVR/reciever or whatever. You can rent PA amplifiers that have USB outputs to read in real time what your output looks like in power and the waveform. Learn how to connect them up and use that software and you will see in real time what is required for your amplifiers to do with your speakers, in your speakers location, in your room with whatever SPL level you require. Very educational, you will have the results in real time what is required for amplification. Before strapping up those pro amps, read up how to do it and program the amplifier to set a limiter to your speaker maximum power level (or RMS rating) also set the high pass filter to filter out frequencies below the rated bandwidth of your speakers to prevent woofer damage. Once you have it programmed, if you like you can crank it up a bit to "see what it will do" at max power but pay attention to the output limiter light! Red is bad! The good news is not only are you gaining understanding, it is rather entertaining to be loud and stupid "for science"
If your ears are ringing but the limiter never flickers--congrats, you have more SPL capability than you can use...
Sorry if this information annoys the mall parking lot audio gurus... 100 watts, 1000 watts or 10,000 watts don't mean anything without all the other factors in the calculation. If you require one number--I'd say 43--it is always the answer.