His contract is excellent value. He's not a perfect player, but I think people make assumptions about his game based on size and bad comps.
He's not a "natural" playmaker, but yet he averaged 6+ assists last year. Not exactly Brandon Bass.
He's too short, yet he gets to the line 5 times per game (where he shoots 87%)
He's a chucker, yet his career splits are 44/37/86
He also appears to be happy enough coming off the bench, given minutes
Would I pay him $10M+? Maybe not, but at 3 years $20M he's an absolute bargain. You're talking about a guy in his prime with enough offensive ability to score 20/night efficiently. There would be nights when Thomas + Smart would give the opponent fits.