i think on a car the modeling prosses is the most important to make all the details and gett a realistick feel overal. the material is just a finish tuch to make the car belivable and nice inn the render.
but a car can look awsom in grey if it is great modeled.
there aint much texturing involved in cars. it depends more on materials. a good material is important to achieve a good looking result. a scene can be as easy as a photo. as inn the tire and rims render you have.