I don't understand your concern. The RS is still a limited production vehicle. They are selling a lot more regular impreza's, now, but they look substantially different than the RS, especially the new ones with no hood scoop.
Why would people looking to by used models decrease the rarity??? It's still the same number of cars on the road.
Also, you can't simultaneously complain that there are getting to be too many, and that SOA isn't bringing performance models over. The ONLY reason a company will offer a performance model is if they get high sell-through on the regular models.