I’m in the Denver area and have had a race at every track this year. I can tell you that the Tag groups are consistently the most attended classes right now. Most every race had 10-15 people racing. Pretty exciting stuff.
The shifter classes vary from 5-10 people. Racing at the track at centennial is the most competitive on the front range. Grand Junction probably hosts the most talented (probably start an argument here!) group of folks. IMI is my home track and has the most laid back atmosphere.
I run shifter and I love it. Right now I’ve got some transmission trouble that I’m fixing, but when I’m up and running I’d be willing to let you take my kart out. Give me a PM.