For Orlando:
Richardson is younger and more athletic that Carter and shoots just as good, if not better. Turk played like a beast with Orlando last time he was there and he wasn't doing so good with the Suns so that is an upgrade.
For Phoenix:
Carter is a good scorer and should look better playing with Nash. Pietrus adds the athletic ability they lost giving up J-Rich, and Gortat can be their starting center and he is legit. Works out for both teams.
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About the Arenas trade, I do not like it. I don't think Gilbert would be a good fit. Their point guard is already a shoot first point guard. All Gilbert would do is jack up shots at and inefficient rate that would be a determent to the team. Getting Arenas would set them back and he has been a head case lately also.
Arenas is nothing special anymore. All he did in Washington this year was shoot 39% scoring 17 a game with a little under 4 turnovers a game. That part of the trade doesn't help Orlando. But I do like the deal they did with the Suns. Having Nelson and Arenas is too redundant, they are both small scorers and Dwight would get even less touches playing with 2 guards like that.