The Spurs just want another big body they can rely on-- someone they don't have to worry about getting caught with a hooker or having rabid pit bulls. They definitely weren't going to carry three point guards into the post season so they need someone useful to fill Wilks' seat on the bench. News flash: Sean Marks is not that guy.
Unlike Malone, Cliffy is under contract with Golden State, so the Spurs would have to give someone up to get him. And due to salary cap rules and such the salaries have to approximately match. Robinson makes 5.3 million this year, the last year of his contract. Unfortunately the Spurs don't have anyone they're willing to give up in that range. Oh wait. There's that one guy they've been trying to get rid of for about a year now. He makes 5.5 million this year.
The Spurs, of course, have offered Malik Rose to the Warriors (along with every other team with an expiring contract). Now, I think it's been well established that Chris Mullin is a horrible GM who has little idea what he's doing. But there's no way he's this stupid. First off, he already has the overpaid player who's supposed to bring energy in Eduardo Najera. Secondly, he has to know that even Isaiiaaiaiaih wouldn't take Malik. That's a big clue right there. Thirdly, one of the other teams interested in Cliffy will certainly offer something better than Rose.
I just don't see a way the Spurs can get him, unless the Spurs have some trade exemption I don't know about.