Eric Gagne was not worth Phil Hughes or Joba Chamberlain. That much we can all agree upon. He was not worth Ian Kennedy or Melky Cabrera. I think most of us can agree on that too.
Sure, it's bad news that the Red Sox got him, and he does bolster their overrated bullpen. But there are too reasons the Gagne trade won't hurt the Yankees:
1) The Yankees are not going to catch Boston. According to Baseball Prospectus, the Yankees have just a 5 percent chance of winning the A.L. East. They should be focused on the Wild Card. So Gagne shouldn't affect the Yankees unless New York ends up facing Boston in the ALCS, something which has about a 10 percent chance of happening, at this point. Cleveland didn't improve at the deadline, and that's more important.
2) Frenchy ain't what he used to be. Leaving aside for the moment the obvious injury risks, Gagne's K/9 rate is down to 7.84, off from his career mark of 10.23. His WHIP is 1.05, still quite good. But while dominating the National League from 2002-2004, he posted a 0.83 WHIP. (Strangely, Gagne pitched exactly 82.1 innings in each of those seasons.) Eric Gagne's still a very good pitcher, albeit fragile, he's simply not the monster he used to be.