Temper those expectations. He's good but will need to adapt to the league. The best thing about this signing is tha the Spurs got him for 3 yrs, and under $11 million (from what I've seen) which is well below the expected mid-level exemption most thought Tiago would sign for. This gives the Spurs a little bit of room to sign another player (maybe a SF, or other veteran) and they may still try to bring back RJ (for better or worse).
This is great news for the Spurs. They needed a boost of youth, size and athletic ability and Splitter is all of that. I don't know about twin towers, but I expect him to be a major contributor from the first rattle out of the box.
While I very much doubt that he'll be a starter, he will give Duncan some much needed relief and with the other young guys coming along, the future just got a lot brighter. Think of a lineup of Splitter, Blair, Hill, Anderson, and another shooting guard or small forward. Could be dynamite!