While it's possible that not folding KK to AA preflop is a leak, I think most of us have far bigger leaks to work on. Therefore, IMHO, working on trying to fix KK to AA is -EV when you can fix some of your other, much bigger, more costly leaks. How often do you see KK vs AA, and how often do you C-bet into that calling station? I'd guess the latter is far more than the former, even if you are a good player.