I wet wade all the time when the water temps are in the 60's and the air temps are above 70 or so. It is a comfort and a convenience issue for me, so if it makes me uncomfortable I don't do it.
I regularly fish one river near us here in MT that has a few big rattlesnakes, so I wear waders when I fish there even though I'd probably be more comfortable (temperature-wise) wet wading, and there are places on another river that has poison oak, so I wear my waders when I'm fishing there also.
However, I wore just a lightweight pair of wading boots with neoprene socks, and a pair of quick dryiing Patagonia shorts, last Sunday when a friend and I fished a rather remote small stream in the Crazy Mountains, and after walking several miles on an 85 degree afternoon, I can tell you that even with some smal acratches on my lower legs, I was a lot more comfortable than my friend was at the end of the day.