Interesting points, Obin. I have seen many a Porsche on the autox course driving like it's a Sunday drive: that's why I would typically beat 1/2 the Porsches with my MR2 n/a with almost 200k miles on it!
However, I think that to win at autocross you don't have to execessively beat your car: yes, you do work the suspension and wear the tires more than normal. Bouncing off the rev-limiter will only slow you down. But staying at redline isn't pampering your car, for sure. Slides and drifts are really good for show, but they aren't always the quickest way around the course! My take: a day of autocross will put a little more wear on your car as if you drove the car daily for two weeks.
Also: power to weight and handling have a lot to do with autocrossing, that's why Miatas and MR2's do so well! When comparing an IT prepped CRX to stock Porsches, you're comparing apples to oranges: such a prepped CRX has the obvious advantage. That's why most autox events have different classes, so that similar cars (power, handling...etc) compete in the same class.
I am an avid autocrosser, but plan on doing DE events now that I have a Porsche. DE instruction and club racing maybe in the future.
People own Porsches for different reasons. Personally, if you're not driving your Porsche hard either at the track or at autocross events, I feel you're missing out of the full potential of your car. However, if I had an $80,000.00 car, I don't know if I'd like to risk putting it against the wall. (That's why I'm happy with my 944!!)
Just my humble opinion.
-Z.
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http://www.pelicanparts.com/gallery/Z-man