When you say AMA are you talking Pro AMA events. I live close to Spring Creek which has a Pro AMA Motorcross and is one of the best tracks in the country. Go there for one of there club series races and there are no spectators. The spectators are the family just like karting. The difference is there are a lot more of them. Karting has just less people racing which in turn makes entries more costly. My Son is 8 and is racing motocross. Would like to get him into karting but if you look at it from a cost prospective things do not favor karting in any manner.