Thai stamps also get better prices at auction in Thailand than in Europe. It's because it pertains to the country. Locals, because it is their heritage, participate more actively. Bank interest rates now are quite low. Your money just sits there for safekeeping.
Travel books are very popular because of their age and rarity.
A complete one is Description du Royaume de Siam by Simon de la Loubere. The first English edition was published in 1693 in France and the Netherlands. The book is in good condition with thread-binding. It tells you how to pronounce Thai words, spells out school rules and has Latin prayers in the back. Humidity and heat will eventually get to books kept in warmer climates like Thailand's.