NASA hosts HPDE events at most of the tracks they go to here in the East. We do Time Trials, HPDE at BeaveRun because it is 1 hour from the house. If you want something fast and simple then Pocono is a great challenge as offered by most groups. We run there with PDA (Performance Drivers Assn / pdadrivingschool.com)-great group of folks and reasonably priced. They also run The Glen, Lime Rock and Summit Point.
The advantage of an HPDE is that you need do very little to the car in the way of prep. All you need is long sleeves, pants and a helmet. I agree that seat time is everything in this sport. That is also a reason why I do these lower pressure events-helps with keeping skills sharp.
If you really want to do local or regional SCCA, PCA etc autocross-then by all means. Find a club in your area and go to an event. Try it out. Most important is to observe and learn from those willing to teach you.
Happy holidays