Traffic is awful, my husband and I tried to go to the quilt show years ago. Traffic was so bad we turned around and went home, the backup was several miles out of town on Hwy 20 and not in a hurry to move.
How far out of town are you? Maybe you can ride your bike from where your camping? Parking can be tricky, especially on the side of the road. I don't know about parking areas in and around Sisters that allow one to leave their vehicle and head to the show.
There is a shopping complex outside of town the local grocery store, Mickey D's and some small shops, perhaps you can park there.