I dont understand the point in completely rebuilding when you have one of the 2nd tier building blocks in the league RIGHT NOW.
That's not a bad point. But if Stoudemire is a "2nd tier" building block, he'll hamper any "fiscally responsible" team that is paying him $20 million per year, which is what his next extension will average out to. Now throw in that he's very likely to need microfracture again (since it is a temporary fix), and at least one year of that deal is wasted, driving the effective price even higher. And now consider that his attitude drives a lot "1st tier" players away, and it starts looking like a less than rosy scenario.
Put him on the Knicks with LeBron James and let their payroll balloon to $150 million, and he'll probably do fine. The Suns, however, have to operate within different parameters. The bottom line is that the Suns will have an easier time finding their next franchise player, and their next identity, if Stoudemire is gone than if he stays.
Now, if for some inconceivable reason, Stoudemire were open to taking a slightly discounted extension with Phoenix (say around $14 million per year), that would be a whole different story. It would be his way of saying, "I'm most interested in winning and I recognize my limitations." I think we all know that won't happen, but it would be nice.
(By the way, a lot of people probably don't remember this, but the Suns' last superstar PF had a contract that was below market value, and never once complained about it, even though he could be a pain in the ass in other ways.)