People have sold off go book collections here on L19, for example DrStraw. Some English books are collectors' items, Segoe's Go Proverbs for example. These books sell well. Routine Ishi Press or Kiseido books sell depending on the price asked. You could test the water on the "Trading Post" forum. Japanese books are harder to sell in the West, I think. You might be able to sell them on Japanese Yahoo. To help you could make a list of what you have and the prices you want so interested people can see.