I agree that it makes sense to prioritise system optimisation over expending large sums on new gear. However, for the purposes of my original question, this might be considered just another form of upgrading.
As I said, what I was looking to explore in this thread is how an objective improvement in sound quality translates into subjective personal enjoyment. It’s the physicist in me that needs to examine our implicit and taken for granted assumptions.
I am not sure many people fully appreciated this. Perhaps, my thread title was misleading. Nonetheless, I am grateful to everyone for giving thoughtful and helpful replies. As a result of the discussion, I have at least clarified my own thoughts on the matter. Thank you all.

