I've never exhibited or anything but I've been going to the Harvest Festival every year since I was little, from what I've experience people are always spending money there. Although it really depends on what you're selling, some booths are busier then others. Most of the high end vendors (jewelry, art, inlay woodwork) aren't that busy, but I think they make a profit since most of them I've seen before, so I assume they come back for a reason.
Have you tried e-mailing a couple of the vendors? You can find addresses in the Artist Gallery
, and if you're a first time vendor they give you a $100 discount
Christmas stuff, food, nick nacks, and bed & bath stuff tend to be really busy. Speaking of which I'm craving fudge and pumpkin bread