How good can it get, really? - my stereo sounds amazing!

I’m in the same place you are. Ttook twenty years, but I  can finally sit back and enjoy what I’ve built. Any further improvement would be minor.  
Which won’t stop me from trying different things, just that the days of heavy investment are over. Tinkering won’t set me back much. 
Some suggestions about what to try next, in your situation—-

1. A hospital grade wall outlet— furutech or wattgate. Get one before you even think about upgrading your power cords. They aren’t that expensive. If you can’t hear a difference, no point sinkng money  money into pc’s. 
2. Are your speakers perfectly positioned? Correct distance from back and sidewalls and perfectly angled and tilted? Experiment with that. Even half an inch can make a difference. 
3. Vibration control devices, whether it’s platforms or shelves or footers. My system is loaded with them. Dozens of choices out there. Check out a few. 

 Kudelka813 - yes!

1: Already done. I had some RF feedback issue and replaced the outlet with a hospital grade unit. All gone!

2: I could benefit from some slightly longer speaker cables. I’d like to play with placement a bit but my current cables are just long enough to accommodate their current position. 
3: Vibration / isolation is critical! I could see myself playing around more in this regard to achieve better sound across the board. 
We are in the same page. I like it!

Back at you, Paulgardner. 
4. My speaker cables are lessloss c-Marc. I think highly of them. Check their website — they are quite unique..  Their footers (Bindbreakers) are also highly effective.  
5.  Whether room treatments would help depends on your room. (Duh ...). Books and carpets, books and carpets. Move the furniture around some. Everything else is voodoo, or can be mostly fixed by moving your speakers around. 
6. The floor between your speakers and in front of you r components is very sensitive.  Worth experimenting with it. I got a very clear improvement by placing a teak chest full of books in that location. Much improved sound staging. . 
7. Try shutting down youR power bar or power conditioner when the system isn’t in use. Also, try spraying down the cabling with an anti static,

which sort of makes my point. There is a lot of experimenting that can be done for little or no money.. .   

No point around here isn’t worth missing it seems...If your room doesn’t need treatment because its inherent acoustics are fine...not dead, but fine...it might even sound like a room, then don’t worry about it. If you live in a large tomato can or a raw concrete bunker you might need some treatment...in that case treat it. Moss...grow moss. I’ve worked in recording studios and mixed live shows for decades, and I prefer less dead rooms. Removing furniture and CD boxes and replacing everything with sound deadening "treatments" is simply silly, and if you experience a weirdo with cheap headphones without ear pads listening to a walkman in your room, that’s geoffkait...remove him...the sound will improve immediately.

Somebody is having a Machina Dynamica moment.