Well worth it. Since coming back from injury/changing his mechanics after 2010, his
last 4 years have had K/BBs of 4.92, 3.04, 3.62, and 5.30 this year. He walks very few, and has been hurt by a strangely high BABIP - .325 and .330 these last 2 years, despite the league-wide offensive slowdown. Basically, he's a classic case of being underrated by virtue of your defense sucking. You can figure him for a 2-WAR player even at ~150 IP, with some reason to believe in health upside (200 innings in 2014).
$12M AAV fully values him at that ~2 WAR level, but in 4 years that may look cheap, and his peripherals may suggest that he's actually better than he's performed to date. The Dodgers can afford to pay the going rate for a few 2-WAR players, probably need to replace some of their roster talent, and McCarthy will have the advantage of going against other teams' #4 pitchers, what with Kershaw, Greinke and Ryu in front of him. Looks like a good signing to me.