If the only mileage your car gets is to/from and at autocrosses, I would change more frequently - at least every 6 months. Oil degrades from time and exposure to combustion byproducts as well as from mileage. Call it cheap insurance.
I change the oil on the S2000 every 3 months, regardless of mileage, but I daily drive the car, so it does rack up more mileage than yours.
The wife's car (which sees less mileage than mine and no hard use) gets an annual oil change with extended life Mobil1.