You know, after doing some research I'm beginning to lean towards starting out in a completely STOCK car in autocross, just to get to know the car. It's a totally different platform and one would be foolish to jump right onto the track without knowing the car.
I suppose I need to find out how competetive a stock Miata would run in it's class (E Stock if I'm not mistaken) vs. the older Civic (H Stock)...