I would suggest adding a "Rhine in Flames" fireworks display to your "must see" list. I just posted the following reponse to another question. Be aware that there's also a Rhine in Flames on August 8 in Koblenz (check the link that I inserted at the end) if the timing of that would work better:
Last fall we scheduled a few days on the Rhine specifically to see a Rhine in Flames fireworks display, and it was a highlight of our trip.
For fall of 2015, you could see one on September 12 (Oberwesel) or September 19 (St. Goar-St. Goarshausen). You can watch them from the riverbanks, along with hundreds (thousands?) of other people, which is what we did. It would be fun to book a hotel or B&B along the river and watch from your own balcony, but hotels may already all be booked by now. Or you can book a river boat, and sail down the Rhine right in the midst of the display, which sounds amazing. The hotel or riverboat option would be especially good if it rains that evening (which it did for us in St. Goar). But I have to admit, it really added to whole experience to be amongst the crowds.
The fireworks lasted over an hour. There were four separate displays, starting with Rheinfels Castle "catching fire" ... then fireworks from behind the castle, then from a barge in the river right in front of us, then from somewhere to our left, and then again from the river. The most spectacular fireworks we have ever had the privilege to see!
Here's a website with info on the 2015 Rhine in Flames displays and river boats.
