I voted 25-50%, but the truth is, I just don't know. I mean, I don't see that much difference in listening with my eyes closed or while cooking, for example. Even with my eyes closed I'm distracted by my thoughts quite a lot. On the other hand, I found myself listening very closely to music while I'm cooking, because I'm very relaxed when I do that and most of my brain watches so I don't chop my fingers off, so no distracting thoughts there. Granted, no sweetspot or any of that audiophile stuff, but somehow I don't quite miss it, sometimes. Must mean I concentrate on music, huh?
I don't have a portable, nor do I have a second system. I have an open plan ground floor, so I can listen to my system very well while I faff about. I enjoy the technicalities as much as the next person, but at the end of the day it's music I want to hear, it's making me sing that I want it to do and if in the process I happen to be amazed by the sound of the drum or the cymbals, or whatever, then it's even better. But primarily, I want music to make get in touch with my feelings, not make me analyse it. Not sure it makes any sense, but that's how I feel about it.
A well balanced approach. You'r not as nuts as the rest of us er - me, I mean!