If you’re looking for a fun photography-related way to invest some money, you might want to look into photobook collecting. The Guardian writes that prices have been soaring in recent years, and not just for expensive rare editions:
Photobooks are expensive to produce and, while demand is too small to warrant long print runs or multiple reprints, it is large enough that the books remain desirable, soon become scarce and can eventually be very valuable. This means new editions costing between £20 and £60 can double or triple in price in as little as two to five years. In 10 or 20 years – and if the work of the photographer becomes particularly fashionable – the price may increase even more.
[...] one of the great things about photobook collecting is discovering the work of emerging photographers whose early books may become sought after. A good place to look is among the current boom in self-published titles.
They also list a number of currently in-print photobooks that can help you get started.