If there's enough money to cover everything, then I'd say yeah, sink more money into cars. But if there isn't, school should obviously come first. After you're done with school will then be the time to spend again on cars.
For the time being, I'd definitely stop sinking money into the Jetta though. You don't really know what your situation will be yet, so I'd just save everything I could.
Personally, I'd go with the RX-8. I like 'em.