It seems like all of the Heat's money is tied up into Lebron,Wade,& Bosh,the same argument against having both Peyton Manning & Andrew Luck on the Colts next season. Apples & oranges,but it doesn't leave much money to provide for extra parts like a strong center & point guard,not to mention capable reserves for next season. It also leaves for a lot of one year contracts for the other players,because who wants to sign a long term contract for NBA "minimum wages?"
Miami is more hamstrung with future obligations than is any other team in the NBA. It isn't just that the big three are on the books for $52 million next year. That by itself is not an insurmountable problem because the NBA has a soft cap and Miami is $25 million over this year and contractually obligated to be $20 million for each of the next three years IF they keep the same team or trade scrubs for other teams scrubs.
The Miami contract situations for players 4 through 15 look like the Knicks contracts for 4-15 when Isiah Thomas was mucking things up by giving max term mid-level exceptions to players who were not going to be worth their contract values in their outyears.
The Celtics were able to stay over the nominal cap by dumping expiring contracts to players like Theo Ratliff, and might still be able to do something with the 13 million in contracts to Jermaine O'Neil and Rasheed Wallace, but the Heat do not have any scrub contracts that are suitable for dumping.
So barring some small scale chicanery, the Heat can sign one mid level exception player to a $3 million contract, and additional veterans for a million and a half each. The Celtics were able to sign Shaquille O'Neil for a minimum contract, so, as a contender, they will have first "dibs" on an end-of-the-line veteran who wants to pick up another ring, but such players are few and far between and might not have the skill set that Miami is looking for.