See, I don't agree that the show is "in on its own crumminess." (And I'm quoting that from your post, best12bars, but, this is really a response to a sentiment I've seen a lot of people stating)
I think it's generally understood that the source material/movie is crummy, but, I'd be really surprised if anybody involved with this production would actually say that they think they're doing a bad show (even a 'so bad it's good' show).
Yeah, it's self-referential and tongue in cheek and definitely winks at the audience, but, I don't think Douglas Carter Beane would say he's written a bad book... and all I've heard people say about the music is how much they love it and how it was the one great thing about the movie.
I can concede that everyone's definition of "bad" is different, but, I really don't think this is going for "so bad it's good"... I think it's going for and, in my opinion, hitting the target with let's make people laugh, let's give them good performances of good songs and let's have fun.