You could spend thousands on HP mods and still not have any fun wallowing around an autocross course.
I'd love an extra 30hp, but I think there's a lot more bang for the buck in improving the suspension and getting the power I have to the ground. Some simple brake mods help, too, but they are a separate category. Come to think of it, I don't need big-money brake kits for what I do, but a few things like better pads and SS lines would be a help.
