A lot of people, including reportedly Danny Ainge, have thought about bringing Rasheed Wallace out of retirement. For Rasheed to contribute, though, he'd at the very least have to take Semih's minutes, and possibly his roster spot, as well.
So, in terms of present day value (or at least, value entering this year's playoffs) who could help us win more, Rasheed or Semih?
At the beginning of the year, I would have found this to be a laughable thread, with the answer obviously Rasheed. Now? It's a tossup. Semih is playing really well, and is an adequate scorer and defender and a decent rebounder. He also seems to be getting better. Rasheed stretches the floor more and is a better defender when in top form, but I think there's a legitimate issue regarding whether Rasheed would be in top form. Also, there's the potential chemistry issue, although I think that was a bit overstated.
Gun to my head, I don't disrupt what's working, and I go with Semih.