Let's establish initially that the FX-x3xx series is about 10% quicker than the FX-x1xx series, clock for clock. So, to even out the comparison think of the FX-8350 running at 4.1ghz, and your FX-6100 running at an even 3.0ghz. In effect, the FX-8350 will give you a 36% speed boost in cases where you are hitting the wall in clockspeed.
GRAPH 1: Your first Dolphin graph shows Cores 0 and 2 being hit really hard. These are two of your three cores that have floating point units, so we can say that Dolphin really wants two, fast FPU units as it doesn't seem to care about Core 4. Core 1 that bounces around at 65% usage is certainly hitting 100% for fractions of a second, but not long enough to show up as peaked out in Task Manager, meaning Dolphin also wants a single, fast integer unit, which you have six of. Moving to an FX-8350 will give you more FPUs and integer units that Dolphin cares nothing about, but the clockspeed increase will help out a lot. If I were to estimate, I'd say you'd see your framerates jump from an unpleasant 20-25fps to a reasonable console-level 30fps with minor dips below 30. An i5 3570 would probably push that up another frame or two, but it will cost you the price of a motherboard to pair up with it.
GRAPH 2: PCSX2 looks to be really nicely multithreaded, and heavily dependant on integer units, which you have six of. Performance will likely scale in the direction of clockspeed by probably 25%, plus in the addition of more cores by probably 20%. This is one of those "best case scenario" events that very much favors the way AMD put together their new architecture. Unfortunately, 35fps + 45% is still only 50fps. You'll still be a bit slo-mo, waiting on further plugin advancements to pick up that extra 10fps to hit a solid 60fps. An i5 would probably be worse in this case than your current FX-6100, and a lot worse than an FX-8350. An i7 3770 would probably do really well, maybe even hitting the magic 60fps mark, but with an extra cost of $100 for mobo and $100 for CPU.
GRAPH 3: It will smooth out a bit, but the change won't be anything amazing. An i5 likely wouldn't do any better.
GRAPH 4: You are probably hitting the limits of a poorly optimized instruction set that relies on the GPU. A couple of GPU plugin revisions will likely smooth that out a bit. Core 2 and Core 3 are being hit pretty heavily so I'd guess you'll see a jump to around 25fps with the FX-8350. Probably another frame or two on the i5 3570.
In task manager did you hit View > Update Speed > High? Normal is default, but Fast will help you catch more drastic spikes. Normal tends to smooth spike off a bit. I wouldn't be surprised to see the spikes reach quite a bit higher on GRAPH 2 when set to High Update Speed.
I was huge in to PSX/N64 emulation back in the late 90s. Hell, I was even a writer and head mod for one of the major emulation blogs/forums/IRC back before "blog" was a word.
I've fallen out of the scene, but try to keep tabs on where Dolphin and PCSX2 are heading. They're both slowly coming along, but certainly making progress. I still don't think either is really usable for playing games, but they've been waiting on clock speed increases for so long that just aren't coming. We need a solid 6-8ghz for good Wii/PS2 emulation, and probably around 100ghz or some amazing breakthroughs in parallelism for accurate emulation.
Anyway, yes, I'd say an FX-8350 is your most effective spend in this case. It will not make things perfect though. If you wanted perfect, you'd buy a PS2 and Wii, right?