I have been 1 time and only bought a souvenir cup... and the perks I have been offered, other than the free wrist band for unlimited drinks for registering your card, are a choice of the cotton candy, popcorn, or a free ride on Thunder Alley.
Now I will say that I returned later in the day to pick up my daughter and because I did not have my original receipt for parking ( they can not use your gold pass twice in one day for free parking, you have to have the receipt from the first entry) I was charged $12. I took that receipt to Information Desk at Main Gate and was given a cash refund for the $12. However, I have no idea if I was awarded any credit for Fun Perks for spending the $12 for parking.
I don't know why they won't post a Rewards Chart like my AMC movie rewards card does. But maybe that's their gimmick..they hope we just keep spending in hopes of getting the rewards.