If they're working no reason to replace them, keep your money for new tires or better brakes.
I've gone through many ISIS BB, and the outboard bearing ones aren't a great investment either. I'd gladly go back to square taper but all the development now is into proprietary designs... Ceramic bearings are next on my list for my race cranks (outboard), when I get a chance. Those things are $$$. Hopefully they'll be more durable.
Old-style XT (octalink??) isn't any better, they last approximately 5 months on average. Heck, I've destroyed a brand new one in one race a couple years back...