Boston is in a strange place. They have the pieces to be in the playoffs, but not do any damage. They remind me a bit of the Red Wings over the past few years. Enough good players to limp along and get into the playoffs but then quickly thrown away by the rest of the league.
You could either try to build around what you have or go full blown rebuild and try to ship out those older contracts. Theres probably teams out there that wouldnt mind getting a depth rental player for a playoff run. Do that, get some picks, and build around the younger guys who are coming up and in a few years youll be right back in the mix.