People overrate the out of Diaw. He was pretty bad on defense in each playoff round. It's not his fault against James, Dirk and Aldridge, but Caron Butler torched him for goodness sake. Splitter saves the Spurs defensively more than people can possibly understand (apparently).
Obviously, Boris is the best all-around offensive player on the team, a top-five in the league, really. When he plays to his potential, the Spurs are unbeatable on offense. But without Splitter, there would have been no Finals or WCF in which Diaw could have exploded. Give Boris his money, but don't think he should be seen as a bigger piece than Splitter.
On Hawes, he's awesome as a third big because he's an ultra-rare stretch-five. He can play with both Griffin and Jordan while allowing each to play in their comfort zones. Of course, such a move doesn't put them over the Spurs at all, but it does inch them closer to OKC.