Every so often, the Yankees check in with the Seattle Mariners about Felix Hernandez and ask, "is he available?" And every time, they've always been told "no."
If at some point the Dodgers were to put Clayton Kershaw out there, the Yankees would love to take a run at him. If and when the Cincinnati Reds decide they need to trade Joey Votto, who is a free agent after the 2013 season, the Yankees would be in a position, because their farm system is in really good shape, to load up some of their prospects and take a run at Votto -- and perhaps convince him to play right field because of course they have Mark Teixeira.
They're very comfortable filling in complementary roles from their farm system. If they can add some elite player from the outside, as they tried to do during the 2010 season in a possible trade with Seattle for Cliff Lee, that's when they'll use their prospects in a trade.