Perhaps it would be better to make the change of amours explicit:

http://img138.imageshack.us/i/stormis1.jpg/

http://img708.imageshack.us/i/stormis2.jpg/ (If somehow you could replace the bridge with something more imperial-like and put Vader and the Emperor/Tarkin inside the circled area; I think it could work).

I'm for mixing ships of different eras throughout the saga. It's like a continuity of technology that makes it all more believable, no one just throws his old car just because he's got a new one. That's why I love your mock up, Bingo. I suggested putting EPIII star destroyers in ANH (the ones that patrol over Tatooine, the ones the Falcon elude when they set off), since Tatooine is in the outer rim and the Empire just wouldn't send their best stuff (the rebellion isn't serious till the destruction of the DS, they're just a "hope"); and even putting Republican and Separatist cruisers in ROTJ final battle, for the Alliance would use every ship (even old republican cruisers, used junk) they have at hand for their ultimate battle, they'd throw stones to the Empire if they could!... wait, I think the ewoks did already did it.

But with the suits, it's different, we see no mixing between EPII and EPIII, so don't know if it would work. It's rather stupid by Lucas to show only white armours and not the rest of the Army of the Republic suits, that based on what's been shown in Clone Wars, is almost the same than the Empire suits (officers, guards, etc)...