How much do you usually spend at Tourist Attractions? Is an Annual Pass worth it?

Hello! I've been trying to think of new and exciting things to entertain the kids when school holidays come around again - but I don't have much money to spend on going out to dinner and the movies (it's so expensive these days!) - I'm curious to know if anyone visits the tourist attractions in their own cities - because I have considered getting a Merlin Annual Pass that lets you into the aquarium and madame tussauds and wildlife sydney zoo but I know its not just going to be the admission price I end up paying for. What do you usually spend on a day out at these places? Do you ever end up buying your children the souvenirs/photos they take? Just figuring out if it's worth the money/time/hassle. Thanks!!!