I wonder how much a performance hit we'd take if the ISD's greebles were normal mapped, it'd have to be a pretty damn large texture, compared to shaving off a few thousands polies. If the Normal maps are more efficient, while the hand greebled ISD would be more visually impressive (and thus, better for missions with a single ISD), we could use the lower geometry, normal mapped one for missions involving lots of them.
I'll look into it once the ISD is done though, even if we only do normal maps, I'll need to finish my high poly geometry to be able to generate a normal map anyways