It's totally worth it, but you have to have a plan. There are tons of cool shows and fun things, but they occur at set times during the day, so you have to plan where to be in the park to catch each thing.
Some of the ones I like include:
BMX bike stunt show
Frisbee catching dog show
Pig races!
I don't think they have the bird show anymore, but it was always worth it.
Oh, and the bands -- find out who is playing at what stage so you can catch their show. I always like the Kildares -- great musicians!
And go see the exhibits like the model trains, the giant butter sculpture, and get your free samples of ice cream!
Read the program they give you and plan, plan, plan to make sure you take in all the good stuff, in addition to all the new cars, the midway games, etc.