Hi Maria!
I have not used Volgistics as an administrator, but have used it as a volunteer and loved it. I would suggest creating an assignment for each festival. It may be easier (from the volunteer perspective) to recognize what dates you are signing up for, so you won't have accidental no shows.
My volunteer manager uploaded our pictures into Volgistics, it helped all staff keep track of everyone. As a volunteer manager, I used Altru, and we undertook taking and uploading our volunteers pictures into their Altru profile. This really helped since we had around 300 volunteers- I didn't know all 300 on sight, and the rest of the museum staff certainly didn't. If you have many different departments working with volunteers, this can help with building relationships as well as security. For a large event like a festival, it helps staff to have a reference. This can also help when you have a staff person say "I saw volunteer X doing A.B,C bad behavior, but I don't know their name." You address the issue more quickly and effectively by being sure you know who it is!
Since we had a large volunteer group, pictures became part of a summer intern project. When the volunteers came in whose picture we didn't have, our intern would take them and upload them, throughout the summer. This helped the intern and volunteers get to know one another better, and they didn't all have to be done at once. Since we told everyone the pictures were just for staff reference, no one protested too much. I also sent them an email before we started the project.
Hope this helps!
Samantha