No to Kaman. I'd rather bring Krstic back than him for the same money, that is, 1-2 years at 2/3M max.
If we are spending MLE money on a big, I'd rather try to get Ilyasova or Lamar Odom.
I wonder how much you've seen those guys this season. Ilyasova probably deserved to be named Most Improved Player and is going to get 8M $/year if not more. Odom didn't show anything, not even enough to get a MLE (though he will probably get more on reputation alone).
Kaman is a lot tougher than Krstic.
Odom's year was "strange", but one year before he played very well. If he gets his head straight on basketball he's the best big out there. Of course he doesn't solve the rebound disease, but he can attack the basket at every time, the biggest flaw of the Celtics offense.
Ilyasova will probably get more than the MLE, but I don't think he plays up to that. Of course his game has flaws, but he's a tough player, can shoot and can rebound.
Odom may get more than the MLE, but this season he's ruined his stock a lot, so he could be had for less than Ersan.
Kaman is a good player, so in case he's healthy he will probably get a lot more than Ilyasova or Odom. But he's not better, at this point, than Krstic, who played last year through bone spurs, and who's played on a broken foot in the Euroleague this year. Kaman has dealt with injuries (season ending) this year, is heavier, better rebounder/shot blocker, but he's less efficient and worse shooter.
Our defense won't improve a lot with any of these guys, so we probably need to look out anywhere else for help.
By the way, if we still have any rights on Krstic, could we sign and trade him? He maybe wants to go back to NBA with his CSKA teammate AK47... they might want to go to the Nets. A S&T Krstic for Kris Humphries could work, although I don't like it a lot, there's a lot of posters who like him.