You said to make comments below. So I did. What did you expect everyone to agree with you? As I said autocrossing is not for everyone. What does "plenty" of autocross experience entail?
Also realize that an off road excursion with autocrossing is completely different than an off road excursion with a track day.
And as I stated each autocross region is different. Some clubs I've worked like 30 minutes out on course and we got 9 runs on a 45 second course (The M Club), some clubs I've worked 1 hour and got 6 runs on a 40 second course (
http://www.nepa-scca.com).
It depends on how large your region is. Susquehanna Region (the main region I run with) gets about 60 cars per event. I've attended one DC event and it has over 300 competitors! I know San Fransisco region gets about that too.
And to answer your 2nd question, yes I've been to a couple of track days/schools with NASA. Yes you get more seat time, but that's a different animal, while it's seat time - it's s different sort of seat time.