I didnt sand mine. 11 months later and no scratches. I used 2 coats of primer, 2 coats of metallic silver, and about 6 coats of clear acrylic enamel. If you feel weird about not sanding it, you could always buy some adhesion promoter.
I would sand it down smooth if I were you. Too me it just looks a lot cleaner and more stock. By stock I mean it fits in with the rest of the interior. But either way you go, it will look better than "stock" as it is now.