Funny, I was just discussing this subject today with a hifi buddy. I also think the brain gets used to the SQ hike from upgrades. Over the years, I have done various tweaks and changed items in my system and more or less it has got better each time. Sometimes the upgrade was big and quite obvious, other times more subtle, but in a few weeks I find I 'accept' the new level as the norm, and it looses some of it's wow factor. This wow factor is what you get in a demo in the store, or on first getting new gear at home. It is not necessarily closer to real music maybe? It may be just a bit more detail or soundstage width. Dunno. But as I say, to me it seems to fade in time, a bit like driving a fast car and you don't notice you are driving faster until you get back in the old one.
If you find you are forgetting the gear and chilling to music more than before, then that is a good sign. But will we ever stop looking I wonder? Another bigger subject.
I think it can be an addiction, try new stuff, like hopeless shopaholics who have a house full of clothes still in the bags they were bought in (my ex wife was like that). I have tried to control it as best I can. Now where was the used DAC advert I saw?