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Four days @ the DLR is plenty. That leaves you a week to do other things...
I think you need to determine how much time you want to spend in the car sightseeing, and how much time do you want to stay in one place.
Los Angeles
The LA area has a lot to offer, and there are a lot of things to see - keep in mind, though, that there are a lot of people here, and our freeways are extremely busy. Things to see: Ghetty Center (art museum), La Brea Tarpits (located only 2 blocks from Rodeo Drive) & the Hollywood area, LA Zoo (I like it), Universal Studios, Magic Mountain, Knotts Berry Farm, the Museum of Natural History & Science Museum (both located next to the LA Coliseum & USC campus), side trip to Catalina Island, Big Bear Lake in the local mountains, San Juan Capistrano Mission (one of the 21 missions founded by Fr. Junipero Serra in the day of the Spaniards), Newport Beach, Malibu w/dinner @ Gladstones @ sunset ...
San Diego
The drive to San Diego is very nice, and the city itself is a great place to visit. You could drive down Pacific Coast Hwy, and pass through such towns as Laguna Hills (an artsy area), La Jolla, Del Mar, etc. You can visit Sea World, World Famous San Diego Zoo, and the Wild Animal Park, Old Town (Spanish flavor), Balboa Park (full of museums and beautiful place to see), Coronado Island, etc. San Diego has a LOT to offer. Lesley (Tink33) can tell you more, if you have questions.
Going up north
Santa Barbara (resident expert: Dave (TheLionKing) )
If you drive up the coast, expect to be on the road about 4 hours. You will pass Malibu, as well as the other coastal towns, and have a view of the Pacific Ocean along the way. You can spend the day at Santa Barbara, and visit Solvang (a Dutch community), and see a couple of missions while you're there - depends on what you want to do. You can either return back to LA via the PCH or on an inland freeway, which will cut down your travel time.
If you decide to travel on up north, then I would recommend stopping to spend the night at San Luis Obispo, which is pretty close to Solvang. Then take off the next morning, and maybe stop at La Purisima Mission (I think the most well-preserved mission), and continue up the coast through some neat small towns and Big Sur -- this is the coastline that you see in a lot of movies that show the beautiful California Coastline. You can make it to Monterey & spend the night there.
Monterey
Beautiful city - I love it here -- Visit the aquarium and 17 Mile Drive, as well as the pier (famous Cannery Row). You can spend one or two days here. Just north is Carmel (Clint Eastwood was the mayor here for awhile). You'll see a lot of seals here and sea otters - I have fond memories of watching the sea otters lazily floating just offshore - pretty cool.
From Monterey, continue to San Francisco - you can take the lonnnggg route along the scenic coast, or take the inland highway & cut down on your time.
San Francisco
Another beautiful city - there is a lot to do here, and you can also take a day trip to the Napa Valley & visit one of the local wineries.
After San Francisco, you can either come down to LA, back along the scenic coast (about a 9 hour straight drive), or come back through the inland hwy, which will cut down your time. You can also cut across our rich farmland, and spend a day or two in Yosemite or Sequoia & see the huge trees here & visit our Sierra mountains. Yosemite - LA is about 7 hours drive, and Sequoia - LA is about a 5.5 hour drive.
*****
Magic Mountain is about 1 to 1.5 hour drive from Disneyland, and traffic may add to your driving time. I would leave @ 8:30 in the morning (it opens @ 10am). The drive back should be quicker since you'll most likely be returning after the rush hour time.