GC model RS values ARE already much higher than any other used Subies of their age, and have def depreciated less than the vast majority of 10-year-old sporty cars out there. They are just not appreciating in price like, say a 1980s Porsche 911, which is what some enthusiastic RS owners wish they were seeing (heh, me included). Book val of my 00 RS coupe is already several hundred less than I paid six months ago. Not that I like this situation, it just is what it is.
compare values of similar model year/mileage Outback wags and RSes....you'll see the RS is holding its own pretty well. Be very glad you ain't trying to sell a DSM or a late 90s VW!