We sometimes forget that the whole point about being in the league is winning championships, if you replace Amare for KG you get yourself a highly reliable jumper from the center position, you get yourself a way better defender (to stop Duncan later on) you get yourself a guy who is a no nonsense hard worker (something Amare hardly is... and I really mean hardly), you get yourself a good passing Center (I know he is a PF but in the suns game he can easily be a PF), I mean there is no way you are loosing anything.
The age is the only thing, but what is the point of having Amare for years when you aren't winning the championship, you would just have a nice guy there for years, and never have won a championship (plus who is to say Amare will be that effective without Nash to dish the ball to him, and let us not forget that not so long ago he had quite a big surgery, and normally those things don't go away)
If I am the suns I do it in a heart beat, and laugh my way to a NBA championship (especially if I can keep Marion)