If you are a golfer you could check out: (Sorry only in german!)

http://www.jakobsberg.de/go.to/modix/now/hauptseite.htm

The hotel is halfway between Koblenz and Boppard on a hill overlooking the Rhine. (not sure if this is an area you would consider.) You would definitely need a car! Hotel is an old converted monastery with a large addition. Rooms are nice and very clean. Not a big tourist hotel as it is frequently used for golf tournaments and corporate meetings.