Okay, so I've been taking the comments about masking and i've figured out that I'll certainly do that for a LOT of scenes. Luckily since I still keep the same background, the rotoscoping is generally easy. This allows that previous speeder chase image possible. The area of Coruscant will be mostly gray with colors from the OT only, but at the same time have important things such as skin tones and the fire intact.
I'll post some new comparison images that involved roto work soon.