I have been to plenty that were more than 40 people, I am sure. For the record you weren't around back when I hosted mine Greg, so I'm afraid that while I may have shoddy memory at the best of times, I'm going to go with my memory of the event over yours.
Albert, some of it IS turnover. Pure and simple.
Tank tours are neat idea, has been done before but in smaller groups, but with the spread of the hobbyists over the city, may be better to focus on those who are nearer to the actual meet, or have splinter groups.