the rs comes without turbo. the wrx comes with turbo. if you want to get 200 horses, look in the link section as well as the forced induction section, vendor section. there are about three or four turbo sprchgr kits listed in various stages of power. 200 normally aspirated horses would require some internal engine/intake/exhaust mods. decorations such as cold air intakes, plug wires, shiney pulleys or stainless exhausts aren't worth much hp gains.
If you are looking to stay NA with your RS then i recommend checking out Cobb TUning. They make very good parts and are subaru specialists. 200 Hp, no prob check out the stage 3 power package .... http://cobbtuning.com/impreza/powerpackage3.html
My understanding is that the 00' and up RS cars are not forced induction friendly because they have a MAP instead of a MAF. MAP's don't know what to do when they see positive manifold pressure. They only want to see vac. or 0 absolute anmospheric pressure. (sea level) There are electronic ways to get around this, but a MAP will never be as accurate a device as a MAF, and a MAF will never be as durrable as a MAP.
If I was going to go forced induction and had a choice, I'd go with a 99'. Air/Fuel accuracy is critical to keep the engine together. One thing to consider though is that 00' (and up?) RS's have rear LSD and 99' and prior are open rear diffs.