I don't think it needs more reflectivity. On some parts you can see it's reflective alright, but as it is a white car it is a bit obscured. Did you up the refractive index to 1.6 or so? Soft shadows is a good idea, perhaps some more GI or a fill light to lighten up the dark areas, and above all; a lot of fine grass and some fake rock debris beside the road. And the car is a bit large, or is it?