Sort of late, but here is my reply.
I have the STI Ver.V kit and took some pics of the GTW spoiler. I doubt you can use the upper part to match your own RS spoiler since it looks really blocky. Sanding won't help it I don't think because to get it to look like the RS spoiler would need a lot of sanding and by the time you got it looking just right, the plastic may be really thin. Plus there isn't the third brake light on the spoiler like on the real car on this upper part of the GTW (GTW spoiler has it on the bottom section).
I have found that the kit is pretty descent for a Fujimi. The 5 spoke gold rims and tires are pretty small, probably average at about 15inch if not less. The most disturbing thing on this car is the headlight detail. It sort of takes away the realistic look to the car, a lot. Most parts are molded pretty thick so it bulges out a lot (ie. rear spats, front spoiler). I had to sand some of these tiny and delicate parts down so it can match the real thing. Just have to get some primer and paint on it now!
