When I did the noise maps near the end of the modeling process, I used the same maps in the diffuse and specular slots (technically the glossiness slot). The result was that the lighter areas had some shininess and the darker areas were more dull. I never did fine-tune it, but the intent was to create an overall weathering effect as though interstellar dust, thruster exhaust and that sort of thing had built up unevenly over a period of years.
If I ever get around to texturing the 3ds Max version of this, I'd like to do a full UV mapping of the whole model and then do some really nice, hi-res maps with bolts and rivets, rain streaks and light corrosion (from those brief periods when it was actually planetside), re-entry carbonization, etc. Hopefully I'll get around to that one day.