Anyone who thinks we should rebuild is delusional. As people have already said, when a GM sets out to build a championship contender, he fails better than 90% of the time. The C's tried to rebuild for the better part of two decades, and couldn't come up with anything better than a team losing in the ECF of a very weak Eastern Conference. And while that might have been partially from mismanagement, think about Barkley's Suns, Kemp's Sonics, Malone and Stockton's Jazz, Webber's Kings, Ewing's Knicks, Reggie's Pacers, and today, Nash's Suns and Dirk's Mavs: all teams that were built well but never won a title.
If we go into rebuilding mode, there's probably somewhere around a 50% chance it goes badly, a 30% chance it goes pretty well, a 18% chance we turn into one of the above teams, and less than a 2% chance we turn out to be as good as we are now. And what's the point in that? Especially when LeBron's Cavs and Kobe's Lakers look to get even better over the next few years.