I think you have a great plan. As you have probably noticed, the ICE to Nuernberg usually takes 1:07. The quickest local train connection takes 1:42 minutes, but this connection only leaves once every 2 hours, so if you leave at 9:06, you don't arrive until 10:48. Of course, it is significantly cheaper, since you can get the Bayern Ticket for 2 people. Still, if it your first time in Nuernberg, and you only have one day... if you're not super price-sensitive, take the ICE and reserve a specific train, as you suggested.

The web site for the Tourist Office in Nuernberg is tourismus.nuernberg.de/en. I suggest you look at their "Top 11" list of things to do. If possible, I would take a walking tour of the city - there are several companies which offer them, not just the tourist office - but you might want to make this weather-dependent. After all, the weather in December is not quite as predictable as Southern California...

I am a railroad fan - if you are, I can recommend the Deutsche Bahn museum. If you are interested in the Nazi period, Nuernberg also offers things to see. And if you like quaint old towns and city walls, Nuernberg can certainly accomodate you.

Have fun!