ain't broke, don't fix it. replacing the dampers "just because" creates the potential for opening up a can-of-worms: bubbles in ink lines, broken manifolds, fried printheads, soooo many headaches just waiting to happen.
...although, it never hurts to set a "cap" on it, for the sake of preventative maintenance. 6-12 is way too soon, however. 18-24 more likely, even though they will really last for the life of the printhead.
also, you should also be able to get dampers for much cheaper than that if you shop-around. I was getting them for $5 on my JV3.