I think it will be hard to improve this team much, outside of getting really lucky with Joe Johnson - that's about it, and really that'd be a reach. I could see a S&T with Ray Allen and a couple of throw ins - but once you talk about giving up Perk or Rondo - you improved SG, but by how much? And how do you replace Perk or Rondo? In that scenario is Nate your PG? (And yes Nate is better to have than Eddie. They have Finley to catch and shoot and not play D - and he's better at that and with more size than Eddie. As you see from the rotations - Nate's main purpose is insurance. If Rondo got in foul trouble or injured, Nate is the only guy you can even think about using heavily at PG. Eddie would have been a disaster at PG.)
The Rasheed signing really commits this team to next year. Perk is probably the only guy that could have real value. I think OKC should make a run at him. They could use his no nonsense approach to lock up the middle.
Ray Allen will just be a question of what he'll take to play here. If its a reasonable offer (couple of years, maybe a team option) at 7-10 million per, he'll be resigned. The harder question will be Pierce the year after. To me Pierce is a history guy and would resign with the C's because he's getting high in career totals - but I'm not sure how much of a discount he'll take. I think Danny keeps everything together until he has Pierce resigned - then he can look into blowing the whole thing up with Pierce in the role of Reggie Miller (i.e. the transition veteran.)
As a complete side note - the guy the should move to the bench if they were to move one of the wings would be Pierce. I'm convinced Pierce could be a very rich man's Posey in 08 and that he's more effected by the minutes than Ray Allen is, Ray's conditioning is better and Ray's game seems to result in a lot less physical abuse. I could also see moving KG to the center spot if they moved Perk and could bring in a PF worthy of starting, except I don't think KG goes for it.