Whilst it's obviously a USP, I'm not really sure how attractive the driving position is I can't imagine it makes ingress/egress any easier, and you lose the option to scare a passenger......
There must be 50+. They had a 1 make series for 3 years possibly more plus there were GT3/Endurance cars as well.
My mate won the class b group of the Lotus Championship in one beating Monkey in 2001 and also drove in Endurance races on the continent with an Italian chap after.