The aquarium in Monterey is VERY worth going to. It is world class. However, you do not have to choose where to stay based on the aquarium, as Santa Cruz and Monterey are only about 45 minutes apart.
In Santa Cruz, in addition to Henry Cowell Redwoods State Park, there is the Santa Cruz Beach Boardwalk, an old fashioned, classy amusement park 101 years old, and a steam train, Roaring Camp and Big Trees Railroad, near Henry Cowell ,which makes trips up the hill through redwoods, as well as making trips into town to the Boardwalk. The Municipal Wharf is near the Boardwalk and Stagnaro Bros. takes boats out on the Bay for whale watching.
There is a popular surfing spot at Lighthouse Field. Even if your kids don''t surf, it is fascinating to watch tht surfers from the bluff.
In addition, between Monterey and Santa Cruz, you should visit Elkhorn Slough, where you can either rent kayahs or take a 'safari' boat trip out into the slough to see the vast amount of sea life.
Here are some links to look at....
http://tinyurl.com/cy7nl3c
http://www.elkhornslough.com/
Edited: 10 years ago