I think adding a power amp is a good idea, but not for any of the reasons you're hoping.
Lacking bass in stereo is because you're not using the sub, #1
, and because your main speakers don't have good bass capability to start with, #2
, and likely because the position that works for stereo imaging is about 99.9% certain to not be a good spot for bass in room, #3
. In short, use the sub when listening to music.
Improving dialog is almost certainly a speaker placement and room interaction problem, not a lack of power problem.
The reason to get outboard amplification is to take the load off of the receiver's weak amp section. That should also allow it to run cooler.
My 2 outboard power amps both run significantly cooler than the receiver does. Sadly, only 1 of my outboard multichannel amps is in service now, because the 20+ year old one has developed a buzz/hum, so I got a new 7 channel to take over. When the whole crappy-beer virus scare is over, I'll send out my old amp for repair and then put it back in the system on the FL, C FR, LS & RS, and let the 7 channel drive the SBL & SBR, and TFL & TFR and TBL & TBR so I can then be ready to overpay for a pre-pro.
I've only got personal experience with old Sunfire and new Outlaw amps. I can recommend both, for what it's worth, as long as you understand what stand-alone amps get you vs what they don't.
Just my $0.02