No...its fine for autocrossing. Sometimes it also comes to your advantage. For instance, my RS with the 2.5 motor is considered G stock or STS with the few items I currently have. However, our bugeye OBS is classified as H stock even though it has the same engine/drivetrain.
Often this allows us to run the car in a class with little competition or other cars that have less power. Also, if you're looking at a pre-2002 model, many of the parts from the RS are interchangeable across the Impreza model line.
I'd recommend a second set of wheels with some Azenis or Kumhos and maybe a set of KYB-AGX struts and go nuts. You'd be suprised how well the car will do.