Re visors, I guess they do look mountain bikey and along with my helmet mirror and handlebar blinkie white light I stick on the visor also, they aren't very aero (reducing my top speed attempts by a few kph I'm sure), but I have to say it's great keeping the sun off your forehead and out of your eyes when riding into a lowering sun.
There are a few times i wish I didn't have one when really down in the drops, but for the vast majority of the time they are great in my opinion. Kinda like driving a car without a sun visor.
FYI, at least on the helmet I have, the visor is removable. In rainy, cold weather I take mine off so that I can put a helmet cover on.