Interesting topic but how much of these perceived "improvements" are bias expectation?
I ask because music played on the same modest systems I own never sounds the same from one day to the next. I'll play a record one day and think "wow, that sounds great" and then play it the next day and think "meh". Nothing has changed.....apart from maybe the fridge switching on
I think mood and possibly things like room acoustics due to air temperature changes, etc, probably affect things far more than minor tinkering with electronics.
....and, of course, expectation bias - you change something and expect it to sound better. The next time you play that fabulous sounding record you are disappointed because your expectation has been raised.
Let's turn to another thing I have been thinking about recently, enjoyment. Do I enjoy my music any more these days played on relatively expensive gear and via "perfect" sources (digital) than when I had my first modest Japanese separates system in the 1970's with the record deck often running slow because the belt was worn and cassettes hissing? I don't think I do, in fact I possibly got more enjoyment when things were less perfect. A bit like John Peel's quote about records:
“Somebody was trying to tell me that CDs are better than vinyl because they don’t have any surface noise. I said, ‘Listen, mate, *life* has surface noise”
This is so spot on. Especially re. sounding great one day and then not so the next.
Mood really does need considering. It's effect on our hearing is profound.
I've made so many changes, and bought far too many headphones/amps/speakers over the past few years and can say for sure all of these changes have sounded good, indifferent and bad. When objectively analysed the change in perception is often down to mood.
Of course, some kit does sound better.
Unpicking what is better, expectation bias, reverse expectation bias, mood, too few beers, too many beers, the fridge going on, worse, the same, the recording, the mastering etc is close to impossible.... at times, for me at least....
I think I'm getting there, ever so slowly. I've got into hypnosis recordings lately and my ability to reserve judgement on perceived differences (better or worse) has improved immeasurably. I'm finding differences/preferences I heard prior more often than not simply aren't there or not as I perceived on the second listen.
No, it doesn't all sound the same. That said, approach with a sceptical and open mind as there's many a rabbit hole in this this journey, of that there's no doubt whatsoever.
Edit: I'm going to add to this the possibility of preferring a over b on day one and b over a on day two.
Like food and drink, where what we've eaten or drunk impacts the other, can where our ears 'are at' affect how we hear. I think it can. A day of clattering noise and you'll want a laid back bath of a system. A day of silence and perhaps some dynamics and detail might suit. With all shades between too.
I think
@uzzy is right, reach a place you're happy and stick. That seems like wisdom to me.
Edit 2: a lot, not all, is mostly about how receptive or not we are at any given time. And of course the recording and how that gels with a given system. I've enough headphones now that I can say for fact dependent on the recording they are all my favourite pair