I've been going to the festivals here since 2005 or so, and living in or near Lyons a decent chunk of that time. From what I can tell, yeah, there's less traffic to businesses in town than you'd initially expect for so many people coming in. Though I'm pretty sure the coffeeshops are slammed in the mornings all week long.
On the other hand, I'm not sure this is much different from any festival with physically-isolated grounds plus on-site vending and camping. If people want to buy food, it's right there, and a lot of it's decent quality stuff. There's a guaranteed social scene around the campgrounds. etc.
The festivals I've been to that really integrate the local economy are things like Airwaves in Reykjavík or South by Southwest, where venues are scattered all over town, people move around a lot, and unofficial/free performances are happening all over the place in parallel. Totally different feel to that kind of thing though.
It'd be cool to see Planet Bluegrass coordinate some small-venue / post-main-stage stuff in town with some Main St businesses and really promote it as part of the festivals, or to have an acoustic campground stage scene like you get at Winfield emerge. But I suspect the template is pretty well set here already, and I'd be surprised to see it change much. (Which is maybe too bad. It might be my imagination, but I get the feeling these events are losing some steam and vitality as the festival scene gets more saturated and more people head to stuff like Arise, or to smaller, less-discovered events with more of a grass-roots vibe.)
Listening to:
Talking Heads, _Fear of Music_