From my experience everyone gets the wrong impression about autocross. Meaning the more mods you do the faster you get. Which is true in drag racing, but not so true for autocross.

You can take an expert driver and put him in a 1995 Civic CX and he would prolly beat a novice driver in an S2000. I've seen it.

Also my other saying is that "Spend $1000 on a suspension setup and you may gain .5-1 second on a 60 second course, spend $225 on an Evolution School or $50-100 on Novice School and you can shave off 4-8 seconds on the same course." I know I've done it too.