This has been "collector central" for many years. Klemens and Sabine Stiebler have run a wonderful hotel, about a 15-minute walk from the venue. The discussions among collectors in the bar are always interesting. And the restaurant is absolutely wonderful (a good breakfast buffet, too).
Hotel in Rüdesheim, Assmannshausen und Rheingau (centralhotel.net)
Another lovely, family run hotel just across from the Ringhotel Central. Again, a good restaurant and reasonable rates.
This is perhaps one of the hotels closest to the venue - also a favourite of collectors.
Rüdesheim has over 50 great places to stay. Here's a link you might find useful:
Booking.com : Hotels in Rüdesheim am Rhein .