My first suggestion is lose the car. There is NO PARKING in San Francisco.

My wife and I have gone a few times at Christmas as well. If you shop around there are amazing hotel deals that week since SF is a convention town and there are none then. We stayed in a great corner room at the Stanford Court on California's Nob Hill for about $125 a night. The place was 1/3 full but fully staffed. It was great being greated by name all the time and they had a shuttle ( limo) for free.They served wonderful coffee in the room with a silver coffee service and newspapers outside the door each morning.

As to eating on Christmas day it is not easy. Our choices were either very overpriced christmas buffet meals at the hotel restaurants nearby including our hotel or chinatown. Everything is closed christmas day. We decided to eat in chinatown. I can make some rec's if you want. We also made sure we had some snack type stuff in our room knowing we would have limited choices.

It is a great time to visit SF because the crowds are down. Union Square is all lit up for christmas as are the shops.

Enjoy, David USA