A 200 inning, 200 strikeout pitcher with an ERA in the mid 3's is worth a ton.
Gardner is the kind of player that looked very valuable based on WAR, UZR, and SB, but he seemed to have lost a step in 2013. Mediocre CF defense, 25% CS, his lowest career stolen bases, and a Yankee team trying to get rid of him? Gardner is a good player, but he isn't worth what he was in 2011, and certainly isn't worth a very solid #2 starting pitcher.