I've only been to five expos total (three easts and two wests) but I've managed to attend the last four venues (the ranch, the lake, the fairgrounds, and biltmore). My two cents on site selection, for what it's worth, is finding a location that is used to handling crowds of 1,000's of people made up of a mixture of onsite campers and day visitors. State Fair Grounds come to mind. Not small community fairgrounds (like the new Expo West fairground which is still a major traffic bottleneck), but large ones. Most state fairs have large parking lots (for parking and/or camping), multiple ingress/egress routes (for day traffic), facilities (don't want everyone digging fox holes do we?), and pole buildings (should they be needed for classes, theater, etc).
Don't get me wrong, there is no such thing as a "perfect" venue. Especially for an event like this which has broad appeal across a wide spectrum of people. I know people that LOVE the Biltmore. I know people that miss the Ranch. I even heard a few people who miss the lake site. That said, as the expo shows grow compromises will need to be made. If not a state fair grounds, then possibly a large venue like a race track (don't laugh) which again has a lot of acreage as well as an infield which can often be dug up. Either that or we need to pull a burning man and all head out into the desert and build out own city for a week.