Excellent points and questions, here's my two cents.
Z Wrote:
1) is it actually important to have a favorite band? i take it seriously when someone asks, "what's your favorite band?" i have a definite answer that anyone who knows me knows. my roommate, on the other hand, only listens to about a dozen bands and, over a long enough conversation, will refer to each of them as her favorite.
I don't know that it's important to have a favorite band but to me it's really enjoyable. Some people may approach bands differently than I do. For me, like you, I've been into my favorite band since high school (Dinosaur Jr.) and I think largely for the same reasons as you. They were the first "indie" band I got into (although they were on a major label at the time) and listening to 'Where You Been' was my awakening from listening to too much classic rock. I own everything they've ever put out, collect live bootlegs, imports, etc. I wouldn't want to do that with many bands, it gets expensive, but it's fun to do for one band at least. It's also fun to get really hyped about new stuff that's coming out from the band or solo projects by its members, etc. For example, I can barely contain myself waiting for the reissues of Dinosaur Jr's first three albums at the end of the month even though I already own the originals. I don't get excited like that for anyone else.
Z Wrote:
2) do you think that every band has one person that considers them their favorite? i guess this has something to do with how long a band's been around, which probably has something to do with how well they do critically and commercially.
I think this at every show I go to. I always assume that every band has its groupies that would consider that band their favorite. For a lot of bands, it's probably that these groupies have followed them from the beginning or go to all of their shows at a venue they play often or something. This would be less true for bands that are just starting out but I think if the band has much history at all, they probably have fans that consider it their favorite.