I'd rather tank, get a high lottery pick and go into the summer of 2013 with what would hopefully be a very nice young rookie to help draw in the premium free agents.
How many premium free agents look for teams with nice young rookies?
well when you have the cap room to bring in multiple players, plus pair them with a young stud, I imagine quite a few.
Say they keep Rondo but move Pierce (for no salary past 2013).
That would put the team going into 2013 free agency as essentially this (I used nbadraft.net for the draft picks):
Rondo, Bradley, Johnson, Moore, 2012 1st (Royce White), 2012 1st (Doron Lamb), 2013 1st (say it is 6th pick - Rodney Hood), which equates to somewhere around 20 million in cap space. Plus you would have whatever pick or young player you got for Pierce (say you get something like 29 in 2013, which is Mason Plumlee).
With just 20 million locked up the Celtics could offer full max contracts to Dwight Howard and Josh Smith (who both might want to play with Rondo and each other).
That would give Boston a starting five of Rondo, Bradley, White, Smith, and Howard with Lamb, Hood, Johnson, Plumlee, and Moore.
I'd say that would be a team that could realistically win a title for the next five or six years, especially if any of the young guys pan out.
I just don't see the point in bringing back KG and Allen unless the Celtics are able to land a premier player this summer (through trades or whatever). I mean if Boston could trade for Josh Smith, for example, than it makes a lot of sense to bring back KG and Allen and give it a go again, but if Boston can't land any top tier players, there is no point in bringing those guys back and just delaying rebuilding.