Actually, I do think all my upgrades were for the better, not just for the different. I take unamplified live music as a benchmark, and while I am acutely aware that no system will ever sound as live (among others, also because microphones 'hear' differently than humans), I do think that a system can sound more and more
believable.
I exchanged components because I thought, and still think, the newer ones sound more
believable. More recent upgrades have also resulted in more resolution (timbral resolution and separation of instruments), but resolution is not a virtue for its own sake. If it is not coupled with believable tonality, dynamics, presence it can quickly lead you down a blind alley of artificiality, and then you exchange components because you look for something 'different'.
However, in order to free a path to ever more believability, you need to get the room acoustics right so they do not stand in the way. I have probably spent more time and energy (even though not more money) in the last 6 years on improvements of room acoustics than on improvements of gear. I will, however, concede that not all rooms are as problematic as mine was and thus need the same attention as mine did.
***
Art Noxon of Acoustic Sciences Inc. (famous for his Tube Traps) has this to say (
link), emphases added:
"When an upgrade is made in a system a perceptible improvement in sound quality is usually delivered to the listening position, which justifies the investment. As the upgrade process progresses, eventually a better piece of electronics that "should" have made a noticeable improvement, doesn't. Here's where the evolution of the audio system often grinds to a halt.
"Product reviewers may have given a new piece of gear raves, but what happens if it doesn't make any difference at home? Is there a problem with the equipment, manufacturer, dealer or reviewers? Probably not, but the audiophile may have reached a performance plateau. From this point on any further electronic attempts to improve a system will remain inaudible.
"Lacking the ability to detect any further improvements in their system, audiophiles frequently resort to entertaining upgrades that may not necessarily
"improve" the system's performance, but do create detectable
changes in the performance. However these artifact styled "improvements" become boring after a while, because they add the same accent to all music, making it sonically one-dimensional." (End quote.)
Note the terms "improve" and "changes", which well relate to the thread title. Art Noxon then goes on that you have to improve the room if you want to really improve the sound rather than just have something 'different'.