Unless you are disney obsessed...like most of us here, I would say three is fine and 4 if you have an extra day.
I live kinda close to you, so if you are like me, you go to California for more than just the Disney parks, so more than three or four days might be pushing it if you plan to do other things.
I highly recommend spending some time in San Diego. The Zoo,
Legoland, Whale charter tours, PetCo park, The USS Midway (awesome), and a ton of other things there make it a must for us.
If you are doing a three day, I would recommend two at
DisneyLand, One at DCA. If four, two at each.
Also, keep in mind that some will ask how many days your vacation is and then recommend you spend ALL of them at the DLR. While I admire their passion, this would be a mistake, lots to do and see in SoCal!
