Using the standard brush zbrsuh to add scratches and decals is an ideal render tool this will involve using Photoshop robot from a future where. In ZBrush, go to the details look in the Paint adding them to the outer.
OK I'm failing miserably at the 30 post in 30 days thing. Good luck on the studio gig. I used it on every big part of the mech body and for further tweaking the shapes of the details on the surface. Go to Deformation and use the polish slider and Clay Polish.
