Good question this one, id imagine in a few years it will be hard to get an early unmodified classic impreza, so if u have a good one it might be worth keeping it that way, Personally id like to have a standard, concours series mcrae in my garage.
With plenty fresh imports of the early versions available at the moment we havent really had to consider restoring rusty old shells as most of these cars as a good as some 2-3 year old uk cars, however some of the early uk cars are showing signs of corrosion, its probally about the time to start on the upkeep of special edition such as the mcrae, terzo, ect, ect,
And like has been said on this post already, standard and restored or modified and restored! as long as its done right you cant go wrong.
cheers
Paddy