I'd be interested to know exactly how much of a difference they make. I can't see the shrouds making a huge difference, and I definitely can't see them saving your motor from a temp related failure. Just doesn't seem like they would direct THAT MUCH air to make a huge difference.
I would think there's ample air to cool the motor just by riding. I never used shrouds and never had a problem, except when I was pinned in 18 inches of snow in third gear not moving.... obviously that was just a dumb idea to take the blaster out in that much snow to begin with.
If you do a lot of riding where you're barely moving, I could see it helping a little bit there since there's not much air moving around the motor and the shrouds would direct SOME air at low speeds.
I will say that it's nice not having to worry anymore with my RM. I still stop every twenty minutes or so just to let the motor cool off out of habit just to be safe, but having a radiator is really nice.