If the report of the Celtics' interest in Bertans is accurate, then they must agree with the OP.
A shooter and an insurance big, even if from buyout market (if one of Theis or Kanter goes out we are screwed) are priorities.
I would also add that the Celtics should view themselves as contenders this year, and not just gearing up for later runs. And in that light should maximize the team on all fronts, which should include imho converting Tremont Waters contract this year. Nothing against Wannamaker, but the C's picked a gem in the second round and should recognize it now, not wait. Waters will add much need 3 point shooting, better game management and more spark plug defensive plays than Wannamaker. He's a natural PG, while Wannamker is just a steady, solid all around basketball player, but who I worry may be turnover prone in pressure playoff situations. No doubt Water's will need reps, so the sooner he's converted the better.
Smart may get the bulk of backup PG minutes in playoffs, but I'm convinced Waters could be a major contributor this season and may be needed in the playoffs, with his shooting a part of that contribution.