Definitely! Well worth it - and of course, a must-do for any true Disney fan, at least once in their lifetime. It is, afterall, the place that started it all. There would be no WDW without
Disneyland.
DL is a very different animal than WDW in many, many ways. Of course the first thing everyone thinks about is the size difference - but - and this truly is a HUGE but - DL is located in the heart of an extremely populated area, whereas WDW is not. Let me explain a little first, as you will see why in a moment.
Southern California is really unlike so many other parts of the country. Cities and towns in other parts of the country end, and are often surrounded by green space before you arrive at the next city or town. Southern Cal is truly a congolomeration of many, many cities and towns that all run together - one ends and immediately you are in the next one. Sure this happens in lots of metro areas -but they stop sooner rather than later. In So Cal - you can honestly drive for 200+ miles and not have left the metropolitan area yet. There are five major counties that make up the L.A. Basin - populated by about 23 million people in that general area alone, out of the nearly 37 or so million in the state. Disneyland has an Annual Passholder base of well over 1.2 million people alone - and it's growing all the time.
Just as I have described my own experience of living out there, (and being an AP holder for more than 19 years) - many of those AP holders will "pop in" for dinner, or an attraction after work. Many others will just go and hang out for some shopping, etc. Not only is Disneyland an entertainment venue - but it is a shopping venue, a dining venue - and often times - serves as a "safe place" for kids to go to after school.
Thanks to the extreme decorating that takes place for the fall and winter holidays (Halloween begins right around Labor Day - and switches to Christmas within about 2 days after Halloween ends) December is a very popular time of year for the locals. Both the "Haunted Mansion Holiday" and the "It's a Small World Holiday" overlays are EXTREMELY popular, bringning tons of people in to the parks year after year after year. Both have been done for the past 13 or more years (IASWH for 15 or 16). Let alone the snow on Main Street, and the Christmas Fantasy parade, Believe in Holiday Magic fireworks... and on, and on.
Southern Cal also does not have a single school calendar - but rather many different ones. A number of districts adopted "year round" schedules many years back, whereby kids will go to school for like 8 -10 weeks, then have 2 or 3 off, and then go for another 8 -10, etc. Others operate on a traditional schedule... but it's not a true benchmark for when to expect lower crowds.
Just as WDW is a huge draw for folks from the midwest & everything east of the Mississippi river... DL is a huge draw for folks from the central plains west. It's a driving trip for many of them - and they go!
Naturally the worst crowds will happen in the later half of the month (we experienced the biggest day in their history on Dec. 28th, 2010 when they stopped selling tickets at 10 am having already reached capacity)... but early on it can be very busy as well.
I'm not trying to discourage you in any way - just arm you with information as you plan and investigate such an incredibly AWESOME potential trip.
As far as time to spend there - I would say 4 days is great. That would give you the opportunity to explore and enjoy both of the parks - and get repeat visits in to favorite attractions. Physically the parks are separated by about 200 paces (average man's stride) - and the entrances face each other. Hopping between the parks is extremely easy. (The entire resort is only about 600 +/- acres, and could fit inside Animal Kingdom and it's parking lot). Downtown Disney is located just to the west of the entrance esplanade, as are the three resort hotels. That number of days would allow you to enjoy DTD and the resort amenities as well. Of course more would be great - but it really is a good amount.
Surrounding DL - Southern California has ample other activities, places of interest and things to do as well. Beaches (they are warm in the winter months) are just about 20 minutes away. Of course Hollywood is not far away - and then there are the other theme parks such as Universal Studios Hollywood (it is an actual working studio - you never know who or what you'll see there - and the Backlot Tour is amazing - I worked there in high school too). Knott's Berry Farm is just about 10 minutes from DL, and truly is the original theme park in America. Legoland is not too far south, and then there is Sea World and the world famous San Diego Zoo. If you like skiing - there's some nice skiing not too far away in the local mountains - and of course the various sporting events as well.
Things to think about too:
- Disneyland does NOT have a dining plan like WDW. What they do have is voucher based and stinks... it's better to just pay cash.
- ADR's (called Priority Seating out there) are made 60 days or less (Not 180) - and often are available to walk-up guests (though I wouldn't count on it in December).
- There is no DME-type service from the local airports (there are several), though there are buses that you can PAY for to get to DL. John Wayne (SNA) is the closest airport, but also one of the costliest to fly in and out of. LAX of course has the most availability being the largest. Long Beach and Ontario are great alternatives. You will need a car if you plan on going anywhere else in So Cal.
- Like WDW - anything within the "price distortion zone" around the resort will cost more. The same meal you might buy at McDonald's at home will be 20-35% higher at the location on Harbor Blvd, directly across the street from the park.
- If you have any unused park tickets from WDW - you can turn them in at the ticket booth and redeem them for DL tickets - at least that was still true as of January - you might want to research that on the DL board to be 100% certain.
I'm always happy to answer other questions as they come up.