If you really want to race, I would put your money into you and not the car. Paying for new tires/brakes/maintaince will cost enough. You will get the most seat time that way. Unfortunately, the Mk3 doesn't fit into any competitive entry-level road racing classes because SCCA doesn't like forced induction vehicles. So you probably would be looking at Time trials or track days.
There is some hope in NASA though, if you have a group in your area. NASA is also pretty good about creating new classes so if you had the time/organizational skills you could create a new class for your region. I looked into making a class for '80-92 turbocharged Japanese rear-drive imports but there is a lot to work out (allowable modifications that will "level the playing feild") etc