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

If you’re thrilled with your system- STOP! You are done. Buy music 

I reached the point of being thrilled 4 years ago. Since then the only $ I’ve spent on my system has been to service a 40 plus year old tuner. 

Zavato, I hear ya. The only thing I’d like to explore is going back to an all tube signal path and stereo subwoofers

The answer is almost always your room. If it is not your room, then the answer is likely your speakers and how they interact with your room. Maybe it is your amp in combination with your speakers, and maybe you have screwed that up with a speaker cable that attempts to do something unneeded and screws up other stuff in the process. If vinyl is your poison, then it could be your turntable setup, but ... see above.

I think most people are on endless tweak searches because their acoustic fundamentals are lacking. People with well designed rooms with accurate neutral speakers tend to be "happier" than those without ... and usually just listening to other people's system, or a visit to a dealer showroom reminds them how good they have it.

Buy three aftermarket power cords and put them into the system one at a time. Maybe you will learn something.  

Um, if it ain’t broke... don’t fix it? At some point contentment has to settle in. “Looking” for things to improve when things are just find is a rabbit hole at best, and can be an expensive rabbit hole that may not achieve anything at all. As said, stay with it for awhile, be in Zen mode. Nothing wrong with that. If the time comes, maybe look at a major change. New amp, perhaps separates if running integrated, or just keep what you have as your “forever” setup... nothing wrong with that either.