Would I go to a class reunion? That all depends on what shape my life is in at the time. If I'm rich, successful, happy, etc, then sure. Otherwise probably not. Apparently I haven't outgrown my shallow phase yet
But really I think that's why a lot of people go. Not to see friends you haven't seen in years, but to see how favourably your life compares to others.
Having said that, a friend from high school I haven't seen in 10+ years organised one in London last year for all the South Africans living here now (over 30 of my class! - most of whom I'm not really interested in seeing) and if I'd been available, I'd have been tempted to go.