I hope you don't mean to imply here that Tillman alone would be enough to get Headley back. Or that Tillman could be the best player in a package to get Headley.
If we're going to trade Tillman for a third baseman I'd rather see Headley coming to Baltimore. San Diego, of they are looking for a deal, should be all over that. Tillman would be a really nice starter in Petco Park.
I think Tillman could be the 3rd, or possibly the 2nd if the best player is much better, guy in a Headley package. But he's not coming near even 50% of the cost it'll take to pry him loose. I do think Tillman would have a much better chance at success in Petco than here or any other park, but that doesn't make him more valuable to the Orioles or the Padres. He's still the same person with the same resume and the same trade value.