Diego

IIRC, the shader derives gloss-sharpness from the intensity of the specmap. So the higher the spec intensity is, the sharper the gloss. Try experimenting with high and low intensity single-color specmaps to see how it affects the material. That should give you an idea about how to author your actual specmaps.

One thing that Arcturus found is that mirror render maps respect vertex color so one possible way to add additional modulation would be to vertex paint between a black specular texture and grey specular texture (etc).

(thanks Rebb!)