Hm, interesting responses here! I guess this touched a nerve for some of you. Thanks, everyone.
For me, the cliques and grudges didn't really get to me. I sorta lived and let live... I had friends who were druggies, dorks, Christians, heathens, nerds, outcasts, and one or two in-crowd acquaintances. They would all come to my parties (I didn't dream of drinking back then, so no alcohol) and have a great time just playing... we had a trampoline and big woods and it was just fun to have all kinds of people there. I had a pretty solid identity as a nerd, athlete, and Christian (at the time), so I didn't care much what other people were doing/thinking about me. But I was very curious about their lives!
I guess I have always been a people-watcher.
I guess I'm just really interested in where everyone is at right now, in their "life course" (sorry, social scientist term)... I don't care so much for comparing myself, as just hearing people's stories, where they've been in the last 10 years. Regardless of their crowd, people have probably gotten married, divorced, had kids, lost loved ones... we're all the same. I don't know if other people have that perspective, but that's fine. I know that regardless of the cliques, we're really all in the same boat anyway.
I guess ever since I taught high school, I realized how petty it all was, and how it came down to everyone basically being a kid and going through those years together... even if I never talked to some of those people (my class had 450+ people). Once you teach high school, the whole thing becomes a lot less negative... you see it for what it is, I guess. Maybe not everyone will see it that way, though.
For example, one of my best friends is dying to go to the reunion, because she still sees herself the way she *thinks* people saw her in HS. She's very successful and pretty now, but in school she had the glasses/braces and was socially awkward. She's bitter and wants to shove it in everyone's face who snubbed her (in her mind, they did). Fine and all, but that's not my thing.
More info: 2 of my closest girl friends are from HS, and we all call/visit each other several times a year, if not more often. We've done that since HS (yes, without the use of Myspace!).
I've also kept in touch with 3-5 of my most important teachers since 6th grade, and even taught alongside some of them when I went back to my old district. They're now my friends. So I wouldn't be going back to see old "best friends" or teachers... they never left my life in the first place.
Basically, it's sheer curiousity about these people with whom I grew up. Not bitterness, not a need to brag, not my own insecurity or regrets or grudges. I just want to see how everyone's doing.
But is that worth $450?