Exactly right, celtic green.
They do need Bosh, especially come end of season when it's winning time. Just look at how good all the best teams are at the pick and roll game. Bosh has good mobility and he has good length to disrupt passes as well. He is one of the best pick and roll defenders in the league, even the commentators say that. On offense, he keeps the bigs out of the paint with his mid range game, freeing things up for the best slashing players in the league to do what they do.
In saying all this, he could not defend Duncan at all. That's why I propose an actual Center like Greg Oden to come in next season. He'll be cheap too. I think if Miami add that element, chalk up another championship. Perfect complement to Bosh.
I would say they keep the current team. They have good enough on-ball pressure with Chalmers and Cole who are developing all aspects of their games, they have enough offensive firepower, they would have enough size if Oden comes in, they have good defensive personnel and loads of experience, coaching and leadership.
From a financial standpoint, you would think Arison would want the success to keep rolling because he know he has a good thing (possibly a record-breaking thing) going on. I propose--ideal circumstances--amnesty Joel Anthony, get Oden in for much the same money; pick Chris Andersen up again, but he will want more than the $700,000 he was on this season; pick up Howard (one more experienced head can't hurt); Varnado (shot blocker), Harrellson (floor spacer); do whatever you want with Harris (floor spacer); not that those guys really matter, but it's not like they caused any problems last season so keep them; and that's the roster. Arison will have to put the hand in the pocket, there's no way around it, with the cap looking to be around $58.5 million and my prediction for next season's salary at $88-90 million.
Side note, Kobe alone will take up a little more than half of the whole team's salary cap next year.