It depends ... (most unhelpful statement, I know)
If you are going to do more than one activity a day, it would likely save you money. When I did the math a few years ago, my youngest was three and I knew we'd only do one thing (zoo,
Legoland, aquarium) each day, so it wasn't cost-effective.
Many of the individual activities have discounts --
AAA, buy tickets online, buy a day, get a day free -- so be sure to figure out your best overall price.
The only other downside to purchasing ahead is if weather or illness prevents you from attending some of the places, the money's already spent.
PHXscuba