So . . . I'm going to be in the area that week, and have never been before. I'm just wondering what the weather is like, and what the crowds will be like. Any hints on how to make the best of it?
I would say that if January 1 (which is in your Title) is your only day to go to DLR - especially if you want to do both parks - get to
Disneyland RIGHT when the gates open in the morning. The reason for this is that many people who were up until midnight on New Year's Eve are sleeping in and/or hungover. When I was there on a New Year's Eve/New Year's Day weekend years ago, NYE was crazier than I have ever seen it at DL (especially on Main Street), but on NYD, the park was close to empty UNTIL about 12 p.m. or 1:00 p.m. Then, all those people who had been sleeping in suddenly piled into the park. So here is what I think you should do: I would suggest getting into Disneyland when the park opens in the morning, while there are still not too many people there, and then at around noon or 1:00 p.m. when the hungover people start piling in, head over to California Adventure, where it is usually less crowded than Disneyland anyway. Then, if you can, go
back into Disneyland later in the early evening and stay as late as you can BECAUSE a lot of people will have left for home by that time, if they have to work the next day. I mean, there will still be a lot of people there because folks probably have a long weekend. I cannot imagine who would be working on the Friday in between New Year's Day and the weekend, but I know some folks who actually have to work! So SOME people will leave later in the day on January 1st and you can capitalize on that if you go back to DL later in the day/evening.
However, if you are going to be in the parks for more than one day, I think you will be okay. I think a lot of people will clear out of DLR after, say, January 2nd or 3rd and start heading back for school/work. Yes, I know some schools are still out for another week or so, but I think many people will be long gone by January 4th/5th. Just my hunch!