In some situations you may want to take this trade. But since you have the team you have (very good team by the way for the 6th in a 10 team league) I think you don't pull the trigger on this one.
All this is based on last years stats obviously. But, I figure you are more than where you want to be on REBS(O/D) and did a fine job spreading the REB across many different players and positions, not sacrificing FGS and PTS everywhere you pick up REBS. BLKS are lacking but STLS are decent. ASTs are always tough to judge but you look OK since Diaw and Garnett are Top 5 in AST for all Fs, and Pierce is getting you 5 AST a game at the G/F. But, where people usually pull away with the AST category is in the guards. Hinrich and nelson give you 6 and 5 a game which is average, but not what you want from your highest producing AST Gs. So, while you make up for most of AST with your Fs, its still a little short.
Anyway your big ? is scoring. On paper babsed on last years numbers your scoring looks very solid. But, can Butler, Nelson and Diaw follow up this year from each of their break out seasons last year? That is a huge question. If so then you're all set. And I think they all get better. Diaw could see a trade and that could be interesting. Another thing: Garnett's scoring has trended downward along with his interest in playing with that team. But it is his contract year, and even though he doesnt have to prove anything, he may be inspired and pick it up, or he may keep declining. We'll see. He'll still be a juggernaut on your squad though.
Either way, all that being said, your team is well rounded and is competitive in pretty much in every category (some better than others). There is no reason to trade Garnett for that cast of characters. You're essentially losing Garnett to gain Artest. Who knows if Nene will be back to where he was 2 years ago. Even in that year he lost nearly 10 min/g due to K. Martin and his numbers suffered in all categories vs his 03-04 season.
But your team has all the major categories evenly spread out throughout the entire roster in such a way that you're almost in a position where you can't make a trade that benefits your team.
And get rid of Dunlevy first before Perkins. He's giving you blks. Dunlevy gives you TO's and missed 3s