Your relationship to new music can be a sign of all sorts of things. And indeed, those things might include a hardening of the heart, or a lapse into nostalgia. But those are not always or necessarily true. A combination of the presence of so much new music, and so little time to experience it, along with just simple things about how we change as we age ... all of those are equally convincing explanations, and they do not require a hard heart or a move towards comfort consumption.
But I hear you. I can remember, during the height of my concert-going days (mid-70s to mid-80s) thinking I never wanted to reach the point where I didn't go to a gazillion shows. It was easy to think that back then ... concerts were among other things an escape from work, and I was young and thought nothing of sleeping overnight in line, or standing on a concrete floor for hours, or just banging violently against fellow moshers. The fact that I attend few concerts now, though, is less a case of my hardening heart, and more a case of my being 60 years old.