Dust and gravel would not leave visible nicks and scratches at all. Maybe some fading or discoloration along the forward-facing surfaces. Nicks and scratches visible from these distances are more likely to be caused by EVA pod collisions, docking mishaps, or the occasional chunk of orbital debris. That's why, after thinking it through, I've decided the nicks and scratches currently shown are excessive. They need to be minimized and concentrated in places where such wear and tear is most likely to occur, i.e. around the EVA pod hatches, the rims of the lander bays, and the edges of certain hull plates.