Both sets of dates will be packed, filled to capacity type crowds. So if you really want to spend NYE at DL, I would go, you won't find it probably a whole lot, if any less crowded in the days before. Basically starting the week before Christmas, through New Year's Week, will be packed. I would go knowing this and have realistic expectations. I would make SURE you get to the parks at opening, in fact about an hour before opening so that you can line up to get in. And I would bet the park will close to capacity, NYE in particular. So know that if you leave, you may not be able to get back in. If you are staying onsite at one of three DLR hotels that will help you to get back in since onsite guests have priority of getting into a filled up park.
I have been to DL when its packed and WDW during Christmas/New Years weeks. You can still have fun, you just have to realize that rides you want to ride need to be done first thing before the bulk of the masses arrive and that you may not get on anywhere near everything. Think atmosphere not rides! Then spend your afternoon people watching, seeings shows and entertainment and knowing you will be part of astonomical crowds of people. However, you are at DL so to me its worth it and quite fun. Just get there early and don't leave the park. Maybe spend NYE at DL so that you can be sure to be in the park for the fireworks and then spend New Years Day in DCA, hopping over to DL if you can. Because even going over to DCA on NYE could be tricky to get back into
Disneyland later.
Have fun, maybe invest in Ridemax so that you can build a touring plan for your crowded days. It could be the best $15-20 you spend if it helps you maximize your day. Its a program designed by a guy who really knows Disneyland, the crowds and how to best get in what you want to get done. If you try to build too much in, it will kick out and tell you have too much in there. So it really gives you an idea of what you can expect to get done and even builds the plan based on how fast you like to tour etc. As many times as I have been to DL, if I was going during your time frame, I'd buy Ridemax.
www.ridemax.com
Edited to add: If you haven't made a hotel reservation you need to, if you even can. Onsite is probably out and the hotels near to DL on Harbor are probably sold out too. So you will have to probably branch out. If you stay out of walking and ART range, make sure you leave your hotel very early, the lines to get into the parking garage will be long. And remember to allow enough time to park, shuttle in and be in line an hour before opening. I still want to stress how fun it can be, but you HAVE to have a game plan and be prepared. A lot of others won't and it will be a nightmare for them. Don't let it be one for you!
