If the Spurs could get Bosh on the same team with Duncan, Parker, and Ginobili, all in their primes, then just on talent alone, this team would dominate, but the response was with regards to the 2010 plan, and I would expect Duncan and Ginobili to be way off their primes by then.
Also, Bosh is not a good passer at all, and I am not sure if he could fit into the Spurs offensive system.
His defense has nothing to do with physical attributes, but more to do with the mental aspect, Amare Stoudemire has all the attributes, but I doubt he could ever be a strong defensive player. Bosh is not that extreme, but does have tendencies of being out of position, out muscled and out worked.
I think he would be a fantastic sidekick, if he was teammed up with, say LeBron James and Dwayne Wade, he would be a fantastic player. I was responding more thinking that Bosh would replace one or more of the big 3.