I disagree on this. I think it's incredibly hard to come by proven, fairly solid big guys. I think the Spurs would think about it looking not only at the possibility of getting #5 with TD, but also past that, where Bosh may not make them a championship contender, but it would allow the team to remain compe ive for a little bit longer after TD retires, perhaps being able to build a new fairly solid frontcourt if Splitter pans out and Blair keeps on improving.
As far as the upcoming season, you look at your foes today and frontcourt size is a huge factor. I personally wouldn't pass on Bosh if he would be available, even though I don't really think he wants to play for a small market. Now, I would do it for a top tier like Bosh. Smith is not top tier, IMO.