More than likely the normal mapping will be completely invisible. 
Re: these three statements, I agree with BlackDove -- I've been replaying the entire retail campaign with 3.6.10 mediavps. when a loki flies past me at full speed during a dogfight, it's true that it is moving too fast to see every little detail -- but there is beyond a perception that what is flying past me is a very highly detailed ship -- the normal maps DO have a not insignificant impact on the appearance of fighters during high-speed combat.
Oi, taking me out of context there a bit.

I'm talking
only about subtle normal maps like the one Scooby has just made for the.....um.....well I have no idea what it's called - the pinkish orangey fighter thing. If I wasn't looking for it, I wouldn't be able to see the normal map at all, let alone notice the detail on it in a dogfight.
I suppose if you have only indentation (which i usually do) then pure white background (pre-normalizing) works best, if you have only bump outs then pure black background (and white detailing) works best, if you have both then grey (128,128,128) gives best of both worlds.
I will agree with VA on one thing, height maps on fighters just isn't worth the performance hit
Huh? No - again I'm talking ONLY about subtle normal maps. Heightmaps are used to enhance and strengthen already strong normal maps, and normal maps really are worth the performance hit if they are strong enough show up as they do in the MVPs. Dial up the contrast on your source heightmap for the spikey fighter thing and regenerate the normal map so that the bumps on the plates are about as visible as they are on the following loki image and see how that looks. If it does look good, keep it. If not, there's no point in using a normal map for that fighter at all.
Anyway, since apparently people don't seem to like the slight texture on the lokis normal map, here's the new version where the roughness has been removed, and I fixed a couple of other things I forgot about in the previous one too.

Download:
http://www.sectorgame.com/ti-file-dump/VasudanAdmiral/FSU_Fixes/NewLokiNormalMap.zip (Might need to copy+paste the link)
Oh and as for the 'level' ground to use - IF you intend to create a heightmap to use in conjunction with the normal map, ALWAYS try and use grey on the heightmap - even if you're doing all extrusions or all indents. Herra is spot on. Using a non-grey colour as your 'middleground' on a height map will create really weird map distortions. For example, if I use my loki source map as a height map, I get this:

Notice the weird and silly looking texture shifts around the edges - the game is treating what is supposed to be middle ground as an indent and shifting everything accordingly - because in my source image the middleground is nearly black.
If you don't plan on using your height map in-game, then it doesn't matter.
