I take your point, but monsters like this maraud through quarries, plunging through lakes of mud one minute, then kicking up dust the next. Also, explosively indelicate loading and unloading can alter gravitational mud-slithering, etc., so they aren't average vehicles weathering-wise. I agree about the wheels, though - a sandy colour might be better. Otherwise, a damn sight better than out the box, easily progressed further.
Talc, blown over wet washes can give a matt, dry effect.
Tony.
EDIT. Way behind due to domestic cosh. Posted as I read but I see you mention talc, later. It's very good for when roads, etc, need matting.