Building a championship team is a marathon, not a sprint.
Both the Spurs and Mavericks have very good interior players, play makers, and shooters. There isn't a ball stopper among them (well... except for Jason Terry maybe, but he's a 6th man).
I trust Donnie to make the right moves, whatever they may be. He has shown that he has the proper perspective on things (unlike Isaiah). Building a championship team requires luck and opportunistic moves.
Now to throw this out there, I hear Stephen Jackson is available. Donnie Walsh loves him, and had him on the Pacers. Personally, I prefer him over Melo because he's a great defender and equally clutch, and will not back down from anyone. He does not fill a position of need though... he'd be a bench player or he might shift Gallo/Chandler to the bench and start in their place. But he's an example of a piece of a championship caliber team.
Rose is not the answer.