The only value TA seems to have is an expiring contract. Teams around the league by now should know though that he's a slasher that when determined will put up points on the board. The question mark is really just a matter of what mode he's in. As we know all too well, he's a Jekyll and Hyde player.
By now, I feel confident in writing him off as nothing beyond an intermediate role player on a good team. On a team like the 08 Celtics, he had stretches where he took over ballgames, and ballgames that left you scratching your head, wondering why he was even on an NBA team.
I think TA alone could command a 2nd round pick, or two, if we're lucky. But I'd prefer holding onto him unless a much bigger trade involving other expiring contracts (Scalabrine?) can be combined to net a player of significance. It would probably mean adding to the already heavy payroll the owners are responsible for. But it'd subsequently provide insurance for injuries. As we saw last year, even our best players could go down and leave us vulnerable.