If it is a place like Waterway type car wash (they dry the car, windows, etc), they make crap wages. I used to work at one in high school.
That hourly wage is about the same as a waiter. I got $2.15/hr plus the tips. Most the time people would tip a couple bucks to each person working on the car (1-2 usually) and more if it was a full wax or detail. Most only work a couple hours a day also, so the hourly wage is basically all taken up in taxes. Granted on a busy day I could work a couple hours and leave with 50-60 bucks.
So yes, you should tip those guys. If you think they dont remember someone who comes in and doesn't tip or is a jerk you are wrong.
And for the love of all that is holy, PLEASE hold off on the armor all, there are WAY better products that won't leave all your stuff greasy, eventually crack and brown your tires.