Belinelli is the kind of player that's right in the Spurs' wheelhouse. He's a good shooter, a creative pick-and-roll player with solid passing ability for his position and can be hidden with a good team defensive scheme. I suspect he'll replace Gary Neal in the rotation, and if so, he's a definite upgrade. Neal may be a better shot-maker, but Belinelli is a more complete offensive player and doesn't have as many defensive breakdowns off the ball.
What's a little less clear is how Belinelli fits into the Spurs' cap picture. As I noted the other day when discussing Manu Ginobili's re-signing, the Spurs could have put themselves in a position where they would possess the full mid-level exception even after keeping Ginobili and Tiago Splitter. I had assumed the Spurs would target a bigger name than Belinelli with that money, such as possibly Andrei Kirilenko.
But by signing Belinelli, it appears that possibility is dead. It's not clear what exception the Spurs used to sign Belinelli -- his first year is too big for the Room exception and I don't think the Spurs have the cap space to fit his first-year salary in -- but either way, San Antonio is likely losing the full mid-level exception. Either the Spurs used part of it to sign Belinelli, or they used cap space and would only have the Room exception left to use.
This is complicated stuff that may only be fully resolved by the time the new CBA figures come out on July 10, but the rub is this: the Spurs have less means to make a bigger move now than they did before. Belinelli will be a good addition to the Spurs, but consider that San Antonio could have simply re-signed Neal and saved the mid-level exception for someone bigger. That the Spurs moved quickly on Belinelli indicates two things: they felt like upgrading on Neal was important, and they don't have a bigger mid-level target on the horizon. Still, I might have considered waiting to see if something else materialized.