Lets not forget that things are alot different than the days of the explosion of sports car racing. Back then, One did less to their Production or Sedan racer, than you do today to a Showroom Stock car. Safety items were overalls soaked in borax, a roll hoop (maybe) behind the driver, lap belts (maybe) and a brain bucket. You drove to the track in the car, added numbers and classification, taped up your headlights, and hit the track.
In an article about Bob Tulius, his start in racing is described as his sneaking out to Marlboro Raceway in his wifes car without telling her. Blame the cal club, blame the interest of safety, or blame denver, but there is no way one could do the same today. The price of entry, even for the entry classes, is just too steep.
As far as autocrossing goes, remember that whether one wants them on the course or not, those who have made engine, as opposed to suspension modifications, are the most severely punished. Do head or cam work, go directly to Prepared, do not pass SP. However, a suspension that would make Colin Chapman envious might just land you in street prepared. I thought handling was much more important than horsepower anyway.
Finally, remember that nowadays, drag strips and ovals (depending on area) are alot more plentiful than road courses. The death of blue laws have also driven clubs to go more and more out of the way to find locations to hold events.