Will be helpful if you advise what model?
MY00 and below cannot be tuned at all on the stock
ECU...
MY01 and over can, and im sure that tuning a completely stock WRX would net a touch more torque and KW, and probably fuel ecoonomy as well.
But the question remains why? Even in the diesel 4x4 world, if you get your car tuned generally you would want a high flow exhaust to match with it to let the car breath a little better.
Same goes here. If you are forking out over a grand just to have the car tuned (verso or similar) why not spend a tad extra, get the exhaust done, get the rumble everyone wants, and get even more power out of the tune which remains the same cost?
Sam