My family of three (parents in their 50s and our 12-year-old daughter) just finished a 15-day trip in Germany, using Rick's guide for the country. Modifying his 3-week trip for our schedule we flew into Dusseldorf, spent a day with friends in Cologne, drove to Bacharach for two nights, drove to Munich for three nights, drove to Rothenburg for two nights, drove to Wurzburg for one night, took a train (after dropping off the car in Wurzburg) to Nuremberg for one night, took the train to Dresden for one night and took the train to Berlin for three nights.
We had a wonderful time and I won't go into the details of the trip. Rick's guide was very helpful and made our trip far better than I could have imagined. However, would change two things. First, I would keep the car as long as possible. We had so much more flexibility when driving and with less stress than the train. German roads, drivers and cars put Americans to shame, and driving was a fast and preferred way to move around the country. Based on Rick's advice we dropped the car in Wurzburg, which was a costly mistake. Trains are not cheap and we needed to take cabs to and from the stations once we ditched the car. Worse, we were at the mercy of train schedules, which wasted time. The train to Berlin from Dresden was an hour late, causing us to get to Berlin around 2 PM, losing a day for an easy 1 hour plus drive.
The second change would be to skip Wurzburg and Nuremberg, and extend the stays in Munich and Dresden. Wurzburg has a beautiful palace and garden and a castle on a hill, but I would have much preferred to spend that day elsewhere. Nuremberg has the Nazi documentation center, but we learned the same information at the Dachau concentration camp outside Munich. There's not much more that's unique in Nuremberg. Munich is a big city with a lot to explore, and Dresden is gorgeous thanks to a massive restoration program. There are many excellent museums in Dresden, of which we sampled two.
I would also skip Cologne, but we had a personal interest in visiting our friends. Actually, Cologne was comparable to and maybe better than Wurzburg and Nuremberg.