I think it's an interesting idea on paper, but actually seeing everything at hand might wind up getting boring and monotonous unless there are some monkey wrenches or different things thrown our way. I just sure hope to God that there isn't unrealistic freestyle involved, because it makes a truly skilled driver just as good as a 4 year old getting behind the computer and trying to freestyle a RoR monster truck.
If everything is executed well, it may be decent.
I think Monster Gymkhana is a cool thing to try out to test the turning and throttle/braking abilities of the driver at hand. Monster Rallycross will probably get boring because once someone gains the lead after the first lap, it will more than likely remain like that unless that person screws up royally. Freestyle, as I said, will be either a hit or a miss.
If you ever need my help in getting this formed up and running, just let me know and I'll offer my advice and assistance if necessary.