Well, CS6 isn't truly that much different than CS5 but the reason I used to rationalize the upgrade was the move to the new version of Adobe Camera Raw and the fact the upgrade was only $99 coming from CS5.
Well let me be a bit more specific.
I own both and use PS CS6 to do wierd things to pictures of my wife.
LR 4 has eluded me in its use. However I can say I've spent less than 5 minutes trying to read about it.
Will change that when on my Christmas leave.