I noticed you mentioned Christmas of 2012. Christmas is a truely special time at DLR. It is like visiting a different place at a different time. It also draws HUGE crowds. Many locals get an AP just for the Christmas season. I'm not trying to discourage you from visiting at Christmas time, just making you aware.
I also suggest early August as the best time to visit for 2012, given all the variables and other factors. Yes, that is likely to be the hottest time of the year, but if you come prepared you won't many problems with the heat. Plan for 4 days at DLR and stay close (like HoJo). Get to the park early and leave around 12:30 or so for lunch and relaxy by the hotel pool. Take a nap maybe. Come back around 4pm or so. You will avoid the hottest part of the day, and the most crowded. You will be more refreshed and ready to take on the night and I suggest you stay as late as you possibly can. The evenings are spectacular at DLR during the summer.
As for your SoCal trip as a whole, I agree with the PP who suggested you start in San Diego and visit the Zoo and SeaWorld first. You might consider breaking up your 4 days at DLR with a day trip to Universal Studios in between. You can keep your room at DLR. Definately do the tram tour and do it early. Lines form there early and get longer. I've found that starting the trip with the Tram tour makes Universal Studios work better. What we enjoy most there are the "shows". High quality live shows. Take a walk down Universal City Walk in the evening. I like people watching and this is as good a place as any to do it. Food is a bit cheaper there than inside Universal Studios so consider popping out there for dinner.
There are a lot of people who seem to frown on Knott's Berry Farm around here but I really like the place. If there is room in your schedule, I would suggest a visit. They are doing a lot of work over there right now to improve it with several upgrades and updates, while still keeping the nostalgic feel of the park. Don't shortchange your visit to DLR, you still need 4 days to really do it right, but if you are thinking of adding a 5th day, think of adding Knott's instead.
As an aside, there is so much to do around Southern California. You don't need to limit yourself to the major theme parks. In addition to the legendary beaches there is Hollywood, Chinatown, museums and so much more. Not to make things more complicated, but you can really create any type of vacation you want.