There are lots of pub sessions for which you don't need a camping ticket but to get on the official camp site you need a season ticket. The camp site is on a bit of a slope and still a bit of a walk into the town centre.
You might decide it is better value to camp outside Sidmouth and use the bus in. ( parking is a problem ). Then you can pick and choose what you go to and have a day off if you feel like it.
Do you want to
Dance
Sing
Play
Listen to concerts
The answer to that might decide what you do.
FloraG.