OK I'm typing this as I listen here, so this is gut reaction, nothing well thought out.
NC
Sample 1: Too sinister for NC I'd have to say... I think if any empire is "sinister" it's the evil empire TR.
Sample 2: I definitely thinks this fits the NC. The timely flourishes fit the NC firing style and it kinda feels like the Rebel's theme song.
Sample 3: Wow, a final fantasy song I don't recognise? I could see this as a sanc song for NC, kinda has a "preparing for battle" feel.
Sample 4: Good Victory song.
TR
Sample 1: Cool song, nice regal feel, I'd say Sanctuary.
Sample 2: Oh yeah, TR battles... nice.
Sample 3: It stays major enough to bee a victory song, or possibly just an Empire Theme would work better because of the minor parts.
Sample 4: This one is DEFINITELY a victory song, and it fits the TR too.
VS
Sample 1: I'm thinking sanctuary music on this one, I'd agree that it fits VS as well.
Sample 2: yeah, I'll go with your description.
Sample 3: I'm not really feeling vanu on this one, from the reedy sounds (cool but dunno about vanu) at the beginning to the drum rolls and lyrical tune. I'd almost say more of an NC (they're supposed to be the guerillas right?)
Sample 4: I definitely think sci-fi scores have good selections for the vanu. This particular piece would be a good victory piece for Vanu I think. I wish the hand off to the trumpets was a little smoother. They took a long time on that crescendo, it's sad to waste the good buildup the strings did and start from scratch again.
I'll think about some actual suggestions, hope this helps!