Bynum seems like he is worth the risk. Now sure, even if he returns to form, Boston isn't going to win a title next year, but the pieces would be there for a title core going forward and I believe the rest could be added with all of those extra picks (either by trade or hitting on one of them). If Bynum stinks up the joint or can't even play at all, then the team is still bad and you don't have any long term cap problems. Basically no harm no foul.
That said, I'd rather sign Oden then Bynum, but either one seems like a good risk to take as long as you weren't giving up the farm for them.