Well there is about 4000 members here, if something was really organized and hosted by this site & USA GasGas, Gofasters, etc I wouldn't see why you couldn't draw 100+ GG enthusiast out for a Friday, Sat/depart Sun deal.
You would have to email all 4000 members here, put it out on the websites, maybe the rags would mention it and generate a flyer with details,events,etc.
It would have to be made to be a big deal, not just me & singletracker saying we are meeting up in IL for a ride and everyone invited. This would be more than a ride, it would be the premier offroad gathering in NorthAmerica (get them Cannucks to come also
A site like Casey IL could pull it off with with space and their well respected motocross/GP track & on par harescramble courses that are somewhat a challenge but not overwhelming.
Another place that could pull it off is ABATE of Indiana ground in Bedford IN (Lawerance county recreation park i think) where a GNCC was held this past yr. Both have indoor bathrooms, electric & all the room ya need.
All guys would have to do is take a few days off work to come to a huge GG event...shoot it would be fun