The specular map would have to be greyscaled, then to cause less lag (and to simply make it look less clogged up) negative it so white goes black and black goes white and all should be ok.
Also, don't apply an alpha to the specular map cos then it covers it all up.
And it only looks really good if there are seperate panels. Like on DJ's Galaxy (pic uploaded). Look at the hull plating on the saucer. The brighter panels are white on the specular map and the darker panels are black on the specular map.