As a few have nicely outlined here, there are cap limitations that make it near impossible to sign Pietrus to any more than the minimum. I feel like people are just coming up with #s that they think are "fair" or what he is "worth" but don't understand the Celts cannot just give him more than the min. without dipping into the MLE or BAE which they really don't want to do. Pietrus and his agent know this, trust me. Not having heard from the Celtics means nothing other than they have to take care of their own higher level free agents first (Ray, BB, Green) then see if they can entice someone like Terry to take the MLE and someone like Camby to take the BAE. Only after these issues are done, will they fill out the roster with vet min contracts. They cannot go over the luxury threshold or they will lose the ability to have the full MLE available.
Also, since Moore's deal is not guaranteed until after the summer leagues, they need to wait to see how he does to decide if they will bring him back. The Celts still have interest in Pietrus, and Wilcox for that matter, but they are low on the list of priorities in terms of signing order. You don't sign BAEs and Vet mins first, those are the last guys to sign. With the new CBA, the order and priority for the Celtics are pretty much predetermined. They aren't going to just go offer this guy or that guy because they like him, the cap is very restrictive.
I personally would like to see Pietrus back, IF, he will take the minimum. That doesn't mean necessarily that I think he is only worth the min as a player in terms of his ability, but rather that that is all the Celtics can afford to offer him. If he wants to be here bad enough, he will take that deal, if he wants slightly higher money, he will need to find it elsewhere.