You can easily do a 2 to 3 week vacation in California with the Main Focus on Theme and Amusement Parks, plus some amazing sights along the way.
I am going North to South, partly due to the drive down the coast allows you on the ocean side. The Northern segment needs to be down in the Spring/Summer/Fall to match all the park's Operating Schedule.
Fly into any of the Bay Area Airports (SJC, OAK, SFO), and I would get a room not in San Francisco, but the San Jose/Santa Clara area, you will get a nicer Hotel and parking for your rental car. Plan to buy both a Six Flags Combo Pass and a Cedar Fair Platinum Pass to save money. From your Bay Area hotel, visit the following Theme Parks. Six Flags Discovery Kingdom, California Great America (CF), Gilroy Gardens (CF) and Santa Cruz Beach Boardwalk. You can also check out Six Flags Waterworld. Other quirky things to see include a tour of the Budweiser Brewery, the Jelly Belly Factory, Winchester Mystery House and the Mystery Spot. Take a day to check out San Francisco, such as Alcatraz.
Take a drive down the coast, maybe a night in the Monterey area, check out the Aquarium, Fisherman's Wharf, and the 17 Mile Drive.
Then head for Cambria and the Hearst Castle.
After that keep driving down the coast on the 101 to Ventura, and then take the 126 to the Valencia/Santa Clarita area. There is a neat Train Museum in Fillmore off the 126. Spend a couple of nights in the area and check out Six Flags Magic Mountain and Hurricane Harbor. Also you could visit the Ronald Reagan Presidential Library and the Nethercutt Automotive Museum. Then head to Universal Studios Hollywood, spend the full day there and then get a nearby Hotel for one night. That morning, head to Hollywood for a few hours, the Santa Monica Pier and its Pacific Ocean Park, then drive down the coast to include the Palos Verdes area to Long Beach. Spend a night or two, check out the Queen Nary and the Aquarium of the Pacific, drive down the Pacific Coast Highway to the Huntington Beach area.
Then the short drive to the Anaheim/Garden Grove/Buena Park area, Spend about a week here, look into a Hotel with a kitchenette, plenty of moderate priced Hotels are in the area, many within walking distance to the DLR. Things to do other than the two Disney Parks and two Knott's Park's. (Both CF parks, so you already have the pass), Three Dinner Theaters in Buena Park, and the new Butterfly Pavilion should be open (currently under construction).. The Discovery Cube Science Center is great for kids. Three different Outlet Malls are a short drive away. Also plenty of different sports venues are close by. Also famous Missions are nearby. You could also add Adventure City and Castle Park Amusement Parks.
Then head south down I-5 to the Carlsbad area, and check out the LEGOLAND Resort and its three parks, I would spend at least one night in the area, if you have young kids, this is the one on-site Hotel I would stay at during your visit.
Then head down the Coast Highway to San Diego. Here you will find SeaWorld, the San Diego Zoo, Aquatica water Park (SeaWorld) and the Belmont Park Amusement Park.
And then fly out of SAN or back to LAX. (LGB and SNA are good for connecting flights back east)
So that is 10 Theme Parks, 5 Amusement Parks, 5 Water Parks and much more.
Of course, you can cut off the Northern California Parks and just focus on Southern California. And if you time it right, you can do one or two County Fairs.
Plenty to see and do out here, and MUCH more variety than in Florida.