I have booked all my hotels for my mid-May German vacation, but one. It seems that on May 14-16th all the hotels I check in the Rhine Valley are already booked. Is there something going on during that time? Mostly I have looked around the Boppard and St. Goar areas.
Robert, Have you checked lodgings in Bacharach? It's also a very convenient location for touring that area.
The St. Goar website shows, under events, 15.05.2011 Guided Hiking, Auf alpinen Wegen zur Burg (On alpine paths to the castle), but I don't know if that is enough to fill the hotels. Have you tried the hotels, pensionen, etc under Übernachten on www.st-goar.de. Boppard is having a public city tour on May 14. The list of accommodations for Boppard is under "Gastgeberverzeichnis" on www.boppard.de.
As long as we are discussing alternate destinations, I would agree with Bacharch, particularly Im Malerwinkel. There is also St. Goarshausen, across the river from St. Goar, and Braubach, below the Marksburg castle. I had lunch at Weinhaus Weighardt and thought it was nice enough to come back for a stay, sometime. There is also Oberwesel, although I would not recommend it as most places there look overpriced to me.
I just checked www.hotelscombined.com and found 15 hotels in Boppard available from 5/14-5/16, 12 of them $100 or less, only 7 sold out. I suspect that the Bundesgartenschau (national gardens exhibition) in nearby Koblenz may be the reason that anything is sold out.