I say race your car, bone stock. It will be the most competitive for the least amount of money. I won't tell you to buy another car to autocross, though. Experience is priceless when it comes to racing. Are you going to be competitive with your car off the bat? No, but throwing you in a Miata, Z06, or CRX isn't going to make you more so. Go out there, have fun, and learn a thing or two. If you want to help yourself, make sure to bump up your tire preasure to about 50psi front, 45 rear. Lock the trans in first gear and shift to second if you need to, but you may not on some courses. Once you wear out your current tires, get something stickier. Or, get a set of wheels for the street and go for low profile 14" tires for your OEM rims. Take off the hub caps while racing.
I took 2nd the last time I autocrossed in G-stock in a bone stock 120k mile Cav Z24 w/ 3.1L & 3 speed auto and Yok Intermediates. So, auto Zetec can do okay if driven well. But I don't expect the car to dominate the class.
Aaron
