"I figure that you have to wear rain gear if it's raining anyway so you've got coverage for your body for that."
I don't find that is true at all. If it is raining heavily of course but there can be water on the road after a rain, or from ground sources that would splash up and get you wet without fenders. I like to get the rainwear off if I can. I agree though that they aren't essential just desireable for me. Most of my riding has been without fenders, now that I have been touring with them for a while, I find myself annoyed when I run into water on a bike that doesn't have them.
The most comon fender problem is that there isn't enough room in the frot fork, there is mounting hardware you can buy or easily make that allow the fnder to start and stop on either side of the fork.