It's perception and our own "threshold" so to speak. Honestly, I remember getting back into the hobby just over 3 years ago and I specifically remember saying, "This is all I need" when I had a U-Turn with a built in phono and a pair of powered speakers, lol.
Well, that didn't exactly pan out. But, once I made the choice that I was going to move up the ladder I did have a budget pool in mind, meaning, I didn't want, or felt the need to spend more than 2-3K per component, that was my "acceptable:" level. Now in the time there have been some components that got a lot of shuffling, while others were very much "one and done". The pool theory being all the components are about the same price level, which in turn "usually" gets a good synergy going within the system.
So ya, there is always better, and that always comes at a cost of course, but that diminishing return issue is a tough pill to swallow sometimes. As
@Joe Mac mentioned, and I've said lately, I'm kind of looking at things in a "just because I can, should I", that doesn't mean it's right, but it's right for me. That "next level" jump
@displayname is looking at is a real thing to, but I think it starts to cater to a smaller and smaller demographic as he mentioned. I mean, I sometimes look at what I have and still get a little sick to my stomach ".........have I really spent THAT MUCH on this gear?!" But hey, to each his own, the important thing really is to enjoy what you have and or can afford and there's nothing wrong with A. Trying to improve your system with smaller, logical bumps and B. Nothing wrong with "oooooh" and "ahhhh"-ing over high end gear