Following strictly the steering principles, speed limitations, etc of Roadcraft will be something many people will find difficult in a car which is quick, rewards spirited driving, often on the wrong side of the national speed limit and has a certain expected stereotypical, aggressive way of driving - which is often opposite to defensive driving systems.
My main suggestion I suppose is that Advanced Driving (from Roadcraft) techniques are more important in a car like the Impreza because it needs more respect, particularly in terms of speed limits and defensive driving techniques - most people are relatively aggressive when driving them, not always to other drivers but "attack" the roads more often, rally style - I suppose
However, the way you drive may may not really be that different from one car to another - it's the driver who speeds, causes accidents and drives aggressively, not the car.
Any pics of the arm rest fitted?
Brian