I almost always wear my helmet. I'm not really that worried about it -most- of the time BUT head injuries are a real risk and greatly increase the chances of drowning. A properly fitting and sized helmet in no way interferes with my enjoyment of kiting so I don't see any reason not to wear one. I don't even notice or think about the helmet when I'm kiting, it's just not something that I'm aware of.
It's just (un)common sense.
I also wear eye protection, but that's because I don't like squinting into the sun and having sunburned eyes. Chalk that one up to pure luxury. I've used SeaSpecs (functional but shitty) and now I'm using Kurtis goggles. Super nice. Before anyone starts complaining about the price... I have excellent vision, better than normal. I place a lot of value on protecting my eyes. I consider the cost of a good pair of goggles to be insignificant when viewed in the context of protecting my vision for the rest of my life.
Yes I wear them with a helmet. I've -never- had them fog out. If your glasses fog up something is wrong.
http://www.kurtisusa.com/