I don't know about the tax laws elsewhere, but IIRC, in the US gains from art are taxed as income, not as capital gains, which would seem to reduce their attractiveness as investment vehicles dramatically.

There are ways around this. Art collectors have started building museums on their properties with limited, often onerous public access:

"Wealthy collectors, of course, have long saved millions of dollars in federal taxes by donating art and money to museums and foundations. But what distinguishes Mr. Brant’s center and a growing number of private tax-exempt exhibition spaces like it is that their founders can deduct the full market value of any art, cash and stocks they donate, even when the museums are just a quick stroll from their living rooms."

https://www.nytimes.com/2015/01/11/business/art-collectors-g...