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. 

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.. .   

This thread seems to be segueing toward a discussion of room treatments. Okay ... fine with me.   

Furniture affects the sound. If you move your furniture, that affects the sound again. How is moving it not a method of room treatment?

Step one: Place your speakers so you get the best sound out of them. It can take a while to get it right.

Step two: optimize whatever else you can, given the room you have. Clearing it of CDs does help, so does moving bookcases and carpets around (it doesn’t have to be far), so does paying attention to the floor in front of your components and between your speakers. An empty floor is bad — Try putting something there. Really ... Try a few different things. (I settled on a teak chest.) And then re-think you speaker placement, because doing step two carefully should send you back to step one. 
Step three: isolation and vibration control. Try different products and approaches. I’ve got isoacoustics footers under my Ref 3a Taksims. I like them fine. Much improved bass and air. That has nothing to do with room treatment, but best to get this factor out of the way before taking up ...
Step four: room treatments.  Look for ones that help. Good luck with that. The best I’ve found have offered only incremental improvements and haven’t been worth it, relative to everything else I’ve done. IMHO looking for room treatments is chasing moonbeams. If your experience is different, happy for you. I’ve heard incremental changes at best, and changes aren’t usually improvements. Diffferrent is not often the same as improved.

finally,

Steep five: play Muddy Waters, Folk Singer all day. Because sooner or later your system’s real stumbling block in going to turn out to be the quality of the recordings you play through it. And that’s the best recorded album I know. (Second place: Laure Favre Kahn playing Reynaldo Hahn.)

Mahgister ... you must be on Tidal