if i maght add someting to the discussion:
battlefront also support specularmaps but they dont ahve a big effect due to the limited lighting system
normalmaps in battlefront work only well with "relief" normalmaps, normalmaps that create bigger shapes dont work that well, probably because the shadow-memory/buffer is too small:

This has been known for awhile. Zeroengine's primitive Lighting system and shaders though make the effort pretty much pointless to go into that much detail.

Normal maps are primarily there to push the small details and "relief" details, the major shapes should all be geometry anyways. Which is what good 3D artists know to do.

The over bumped effect from the normal map is from not defining certain things in the Normal map texture's .option file properly. In that case the bump strength is set too high. setting it at 1 or 2 will give the desired effect, but again the lighting still kills it.