I don't see MIA taking another Wildcat player, which is probably what Spiller would be in our bruiser system. With Ronnie Brown as the between the tackles bruiser, Ricky will be the Wildcat for one more year, and probably keep 4 RBs since we would need Ricky's replacement for the following year, which I would think would be Hilliard and Sheets and drop Cobbs.
But even if Williams went down, I could see MIA using Pat White as the Wildcat in motion while ROnnie takes the snap as the Wildcat guy basically runs in motion to either take the handoff at fullspeed (which Pat White looks the part of) or is a decoy and can become an option to pitch to for a pass, which Pat White looks the part of, or decoy WR that can step back and take a pitch for the pass (as Pennington did to Cobbs last year, which White looks the part of).
So I just don't see the place for Spiller, especially at the cost of a more dire hole to fill like ILB, OLB, NT, TE, FS, WR.