For starters, you only need to please yourself, so if you’re happy or "happier", your system is good and/or improving.
You’re also only as good as your reference. Getting exposed to systems that exceed yours can be useful. So can listening to live acoustic music like piano, guitar, voice, or orchestra.
Expectation bias can certainly come into play, but it should be temporary. Usually if I’m making a change, it’s because I’m trying to eliminate an area of concern, or improve a specific region. It can take time to determine if the change had the desired effect, and did it without causing another area of concern. Give the changes a good long listen to overcome the day to day variables we encounter. Listening is a skill. On any given recording, pick out things you like or dislike about the recording itself. If some of the undesirable characteristics are a repeating pattern, it could indicate a problem area of the room or system (like sibilance or boomy bass)
Most importantly, enjoy the system, enjoy the music, and enjoy the fun of changes. If you’re happy when you listen, all is well. 😎