very true. ask around ...not just subarus look at the hondas or rice rockets... i am sure buying a stock is much more simple and easy to deal with than buying a modded car.Buy a stock RS, get some experience, and then swap it yourself.
From an intrinsic standpoint, its just more fullfilling to know that you built your own car. Its always disappointing to meet people with nicely modified cars who can't answer why they went a certain direction in the tuning or why they chose this part over that part beyond "that's what the shop told me" or "because its this brand."
edit: On another note, its sometimes hard enough to spot issues and problems on a used car even when stock. Add the fact that its been heavily modified and you may be setting yourself up for heartbreak.