I don't belong to a guild, but I have been very involved in dog breed and all breed clubs ... and it's pretty much the same story all over. The same people do the same work year after year.
Some of the best incentives that I've seen is to offer: reduced membership dues for X hours worked at an event, reduced (or free) admission to events that have a fee for X hours worked, a basket full of fat-quarters and/or quilting supplies for the member that sells the most raffle tickets (regardless of whether they were sold, or purchased by the member - they were still SOLD which means income), and finally .... paid dinner at a fine restaurant for all members who work at least X number of hours for the show (in any capacity) (the paid dinner actually attracted quite a few volunteers for us!).
It's also a good idea to collect the names of members who wish to work the show, then "assign" the duties to them as opposed to allowing them to pick-and-choose the function they want to perform. Don't assign the duties until the day before at the earliest (unless the assigned duty requires more advance notice).