I've been thinking about this quite a bit for GC and then Warp, and now I present it here.

Instead of just having "Rebels" and "Imperials", what about splitting it up into the units that fight that particular battle and giving them and their craft emblems, unit numbers, etc.? If movie-specific division names et al can't be uncovered, which they of course in most cases can't be, just make something up. The Spawn screen would have the Class Selection buttons (the ones you hit to select class) bear the name of the unit as well as the unit's emblem.

For example, let's take Hoth. The Order of Battle would be, for example:

   Imperial Death Squadron [Death Squadron's insignia instead of Imperial crest]
147th Stormtrooper Division Stormtrooper
147th Stormtrooper Division Tank Hunter
147th Stormtrooper Division Combat Engineer
147th Stormtrooper Division Scout
60th Medical Unit Battlefield Medic
Blizzard Squadron Walker Commander

   Echo Base 5-7 [or something]
86th Alliance Infantry Division Trooper
86th Alliance Infantry Division Tank Hunter
Molde Engineering Company Combat Engineer
86th Alliance Infantry Division Scout
52rd Combat Medic Unit Battlefield Medic
Rogue Squadron Pilot

(Please don't nit-pick this and go "this class shouldn't be on Hoth" or whatever. This is just an example)

Not only will emblems, squadron markings, etc. look damned good, but this should also add a lot of immersion to the game. Instead of saying "a legion of Imperials", you can say "the 382th Imperial Infantry Legion" or something, and then have the same units appear in different maps.

Imagine loading a space map and seeing Y-Wings and X-Wings with, say, Krayt Dragons painted on the side of their hulls. I think a lot of people would go, "wow, what an attention to detail! The fighters have different crests for each map!". It'd also be nice if, where appropriate, ships had their names printed on their sides. Having a map where you're hunting a freighter named, for example, "Icefield" and actually seeing "Icefield" printed on its side would be great.

Edit: You could, technically, use different voice sets for each unit, but I suppose that'd be a bit too much work for too little effect.