Well, we shouldn't mix up two questions. First, the Perk/Nate for Green/Krstic was great at the time and in hindsight, it was injuries to Shaq/JO/Krstic what kept the Cs from a championship, not losing Perk.
Second, Perk was very good for the Cs, and he's never been the same after his injury. That's why Danny traded him, he didn't want to pay Perk all that money. He deserved a 6-7M per year contract, not 9M, but his play level is more like a LLE player at this point.
That said, I love Perk, and I think all the beating he gets from the media is ungranted, and makes me angry. In fact, right now the Cs could use Perk even at his terrible contract. I've banged the drum of helping OKC to get Asik by sending Houston Bass+Lee, to get back Perk+PJ3+2014 Dallas first rounder from OKC.
Perk could help in developing the young kids during this season. Then, next season he's a big expiring contract to unload at the trade deadline. Celtics can afford to downgrade talent this year, one step backwars to make a big jump next season. And finally, he's Rondo's best buddy, and you want Rondo (and FlCeltsFan, too) happy.