I have very little hope that Wallace will ever become a viable starter again, though. He's declined in points scored (per game and on a per-minute basis) for four seasons in a row. We've seen a similar downward trajectory in terms of FG%, TS%, and TRB%. I'm not sure that many players turn around trends like that.
I'm not so sure. I remember watching Wallace in Charlotte and he looked like a role player until that '09/10 season. I think given a broken roster and the opportunity to be a focal point Wallace might bloom again. That is sort of what happened under Larry Brown in Charlotte. Actually if you throw out Rondo (injury) there are some striking parallels to that team:
Wallace (obviously)
Stephen Jackson (Jeff Green?)
Boris Diaw (Sully?)
and while I'm sure Rondo is a superior player to Ray Felton I believe that in the first part of the season this Celtics team will look at lot like that Bobcat team. We'll play an undersized center in Sully/KO/Hump just like Charlotte did with Diaw.
Now I doubt Wallace will average 18/10 on 48% shooting but if he gets 41 mpg and 12.4 FGA he might get close

The truth is that Wallace was never an all-star. He got the benefit of being played a ton on a bad team. I think he could get that benefit again and show that at 31 years old he's still a very capable NBA player. Something like 12/7/2 in 25 mpg isn't out of the question.
Oh, and my response to the OP is also nothing, similar to the recent posters. I like Wallace, I think his contract is bad but I'd rather try to trade him next year when we're more competitive than give up something to trade him this year. I also think he'll be a strong veteran voice in a relatively young locker room. Something we could use after we moved out nearly all of our established leaders.
Truth be told I'd sooner stretch Wallace's $30M over 5 years and waive him rather than give up an asset to move him this year. That's just me though.