This is all I can think of:
1. Seats to base SVX cloth seats or WRX/2.5RS seats.
2. Carbon/Fiberglass hood.
3. Manual Swap.
4. A/C system (pipes, condensor, and all)
5. Heater core, radio, climate control, and everything else that isn't needed to make the car run behind the dash.
6. Power seat belts to manual belt conversion.
7. Speakers, trunk lining, spare tire, jack and tool kit removal.
8. Aftermarket exhaust (stock is heavy as balls)
I can't think of anything else that's a simple job (or simple solution rather...see manual swap
) that would keep it easily streetable. Some things would already make me not want to drive the car. I had a stripped Impreza, stripped 240sx, and essentially stripped 240Z. I can't imagine the SVX getting the same treatment. The next step after that I'd guess would be grinding useless metal, removing carpet/insulation/sound deadening and replacing with thin carpet, and that's it. Getting rid of some unspring weight would be nice, but big bucks.
Part of the reason why I like this car so much is that there aren't many parts for it. You end up having to have to make your own solutions to things.