Gold is (relatively) easy to store, transfer, hard to obtain, really limited supply -- the qualities that make commodity good money. Uselessness of gold is actually useful here -- transactions with it does not distort markets. Imagine if we used coffee beans as "gold" -- then changes in monetary velocity would impact consumers, who would be forced to stash it.
Sorry, the brevity of that comment apparently didn't convey my point well enough. Real estate is an example of what you theorized would happen with coffee beans. It is a useful resource that is also used for speculative investment. It is something everyone needs, but as a society we have decided its price should also always be increasing. This has a net negative impact on society.
Bitcoin existing doesn't stop people from speculatively investing in real estate, so I don't think people will just start speculating on coffee beans or something similar if Bitcoin goes away.
