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

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. 

If it sounds amazing, then spend your time enjoying music.

My upgrades in the last 18 months included a new DAC/power supply, interconnects and new speakers. I consider them 'end game' items for me, and will be unlikely to replace them.

Have since embarked on a journey of tweaks and their effect on sound. Some turned out to be excellent, some good, some uncertain.

My system is sounding fabulous, and is exactly what I was hoping for.

First climber: WOW! What a view! Being at the top of Everest ⛰ makes me feel like I’m King of the World! 

Second climber: Hey, get a hold of yourself! We’re only at Base Camp ⛺️