yea, you can still mess em' up with enough water and mud direct exposure, ask me how i know .
That being said, it's a pretty solidly built alternator, and it does put out a huge amount of power. sooo... *shrug* it's never a bad idea to have two alternators, since ours is located so low, so if you want, I would buy one, and just keep a spare in the truck in case you kill it on the trail.
I'm tempted to get a better alternator than stock, since I've got a lot of electrical components I've added on (power inverter, usb ports, compressor, lights etc etc). Not that I run them all at once, but I figure anything that'll help the X run a little more efficiently is a good thing. I've looked at the mean green but the price tag is a little discouraging.