If you read Ian Levy's article on Nene at Indy Cornrows, you see him mention the "Player Swap" tool that is hosted by Queen City Hoops. He states that replacing Roy Hibbert with Nene last year would have resulted in 16.5 more wins for the Pacers.
I'm not going to explain the tool because I don't really understand it. I will tell you that it uses a ton of stats (just use it once and you'll see). I should warn you, since I found this it has eaten an hour of my life.