I absolutely share your opinion. There should be more special offers ref. tickets for families (not to mention that families spent more money in a zoo per person then a single person or a couple - "Dad, I really love that plush giraffe!", "Mom, can we ride the mary-go-round for another time?").
Luckily, not all Aquariums have that high entrance fees. As I went to California this spring, the adult ticket for Aquarium of the Pacific (which is better and more diverse then Monterrey Bay imo) was about 30 USD. Also, you've had the chance to buy a combo ticket with L.A.-Zoo, which made it a good value.
And about Sea Life in general: I already wrote and said: It's overpriced and it's boring. Visiting SL Centres around the world is like visiting McDonalds-Restaurants in every town. You always know what you get, but it is always the same.