It depends on what you want to do. If you want a Disney immersible vacation, then stay at the Disneyland Hotel. It has all the old classic charm and Disney theming. We won't stay anywhere else. Paradise Pier is built to resemble the Paradise pier area and Grand Californian is like a big lodge and very elegant. None of the resorts are *value*. We love the convenience of the DL Hotel being at one end of DtD and the Parks at the other and you can walk to the parks and go shopping and have all the perks of staying right there.
I would say go for at least 3 days. That way you get a whole day at Disneyland, the original and a day at DCA, which can be done in a half day if you don't have kids. You will also get to go back to Disneyland, because you may want to re-do some things or catch others that you missed the first day. And you can swim at the hotel or go shopping and check out DtD as well.
DL is our *home* park and we always go for a week, 7 days! We love the ambience of being there and taking it very leisurely, we have no kids so we can just spend a whole day relaxing by the pool if we want. We get to go to the parks every day and see just a little at a time, catch shows or shop...I love a vacation where I feel rested and not rushed. I don't like coming home, feeling like we did not get to do or see everything, even when we have been there so many times. We don't even leave the resort complex.
Rehabs in January can mean no Splash Mt. Last year the entire castle was draped because they were repainting and rehabbing. Expect LOTS of rehabs in the off season, you may not get to experience some of the things you want to. And DCA will be going through some growing pains and will be not *whole* But definitely go on Grizzly River Run and check out the whole Grizzly Peak area. It is so much fun! Disneyland Park has several attractions that WDW does not have and you should definitely try those and Space Mt. is better at DL. Small World facade is a picture worthy spot and the fireworks have that elusive hidden Mickey firework, watch for it! If Fantasmic is up, which in January or February, I don't know, check it out. VERY different from WDFWs. No amphitheatre, so you have to stake out a spot early or stand. It may be on hiatus at that time of year tho.
Get a good Travel book on Disneyland, I recommend "Birnbaums Disneyland" It will help you with planning your days.
Have fun! Disneyland is the Original and the coziest Park. We love it cause it was the first. There is a lot of Magic there. We love WDW for other reasons,(SO much to do, we spend at least 3 weeks or a month onsite
when we go to WDW) but will always plan a couple trips a year to DL!
I hope you have a great time and come back with some wonderful memories of the little Park!
You will probably not recognize it. It has changed so much! I was astounded when I went back after many years of being away, the lean yrs, I call them! LOL! You will be amazed at the way things look and you will have to figure out the whole new configuratoin of the resort, it is completely different!
Mermaid1