Howdy doody my good friend
Dont be fooled by the fact that it's a none turbo. I actually nearly ended up owning 2 Scoobies at one point as I had someone who wanted to swap my Frontera for a Scooby Sport estate. Didn'y have it cuz of its condition.
But to be fair I was pleasantly suprised considering they are a big car. They do shift quite nicley and aslong as you get the SPORT version you will have a nice little switch to flick the gearbox into sports mode which lowers the ratio of the gearbox and makes it accelerate evn faster. Yes the Wagon (estate) will be slower than the Impreza (saloon) as it has more weight but dont be put off at all fella
The best thing you can do as far as performance goes is actually pretty much the same as what you would start off with if you had a turbo. Get the exhaust made staright through for a start, get some equal length headers or even have the standard ones board out, think about a good sports panel filter (cone filters dont work aswell on a none turbo) with a nice 3 pipe mod to the bottom of the air box and a cold air feed. Then think about getting it remapped. These alone should give you nice start and certainly will notice the difference.
2 absolutly huge draw backs with the none turbo's aswell is the brakes and suspension. The front brakes are quite small compared to the turbo and also the rear hasn't got disks, they have drums
The suspension is also alot higher than a turbo so you may find it a bit floaty round bends. So would be well worth thinking about getting the brake set-up and suspension from a turbo model
or if you dont want to go through the hasstle, just look around for sports that have been made the same spec (apart from the engine) as a turbo model such as the WRX or STi
Hope this points you in tyhe right direction.