I can't think of a single reason to turn down any good offer for Valbuena.
He kills us with his "errorless" defense. He adds little. We have somewhere in the neighborhood of 6 candidates to play 3rd. Ok, that includes Olt who has shown little. But seriously, I would trade Valbuena and play Olt every day. If he succeeds and gets experience that matters, good. If he continues to struggle - and that is being kind - we suck more, which is kind of the point right now.
I don't see the value in Stumbles that others do, though I know he is a cheap option.