I've never weighed in on this but am in the "I can hear a difference" column.
As a musician (75 yrs old) I've played in a lot of different groups with a lot of different musicians at all levels. The really good players have a subtlety to their playing - no matter the instrument. What I've noticed is that many of the musicians I've played with who have been playing for many years "think" they play as well as the exceptional musicians and I've come to believe that they simply do not hear the nuance and subtlety of the top musicians. The top musicians DO hear it and learn to apply that sensitivity to their playing. In other words, some people hear nuance and subtlety that others don't. For me that is one explanation for this continued discussion.
I listen exclusively to headphones so listening room is not part of the equation. I also have certain tracks I've listened to for many years and when upgrading anything I always notice a change in different parts of the recording. Some I like, others I don't. I've purchased expensive cables that I didn't like and returned. Others brought a level of sensitivity I hadn't heard before.