Science has done some great work on cognition and sight. In short, your brain scales your attention up and down depending on your free resources. If you get enough motion on a screen, for instance, you won't notice that the colors change in the background because your brain is just too busy to pick up all the detail at once. There's nothing wrong with the system, or with you, it's just that the brain has a finite processing capacity.
Now, let's talk sound. When you set up a new sound system, you listen to your new system with close attention, making it the center of your focus. Your cognition is entirely focuses on the sound coming out of that system. You notice things in the music that you never noticed before. The detail leaps out at you. You made a good purchase.
As time goes by, you don't spend your full focus on your sound. Your brain wanders. You pay more attention to lyrics or remember that you need to take the trash out. With the sound no longer the center of your attention, your brain silently drops details in the music. Your system still sounds good, but you know, it coulds sound better, so you buy some new cables and then listen intently. New sounds leap out at you. You've made a good purchase.
Do you see the pattern? This is exactly what I see among audiophile. "I got this new thing was it was AWESOME." The reason that it was awesome, the reason that they heard things that they never heard before, was because they were paying attention.
One audiophile thing that survives this anaysis is the listening room. For those people who build their own listening rooms, having a place where they can pay attention, matters more than most gadetry.
Am I sayiing that all upgrading is bad? Nope. What I am saying is that the listener affects the sound far more than they think, and that their behavior may make the biggest difference in a good sound system. It's no use buying a $20k audio system if you let yourself get distracted, only to have your brain scale it back to a $1k sound system. Your brain destroys the best specs. If you are ignorant of this phenomena, you can wind up spending money without actually improving your sound, which, I am sad to say, too many audophiles have fallen prey to.