(1) it must take skill to conceive
(2) it must take skill to create
(3) it must be enjoyable for the 'consumer' to look at / experience.
The above hasn't been true in the art world for at least 100 years, as mentioned.
Of course, the art world is made up of a handful of people; artists, rich collectors, critics, museum directors. Where would Tracy Emin and Damien Hurst be if not for Charles Saatchi? The art market is basically a very small group of rich people trying to prove they they have taste, prestige and status.
If a painting by Van Gogh is sold for £100 million and it turns out to be a fake, does it suddenly become worthless when it's still the same painting?
When art came to America.
A mere 105 years ago. Give it another 105 years and people might start to accept that not all 'art' has to be in the form of paintings representing real people, objects or scenes, framed and hung in galleries.
I find it interesting how some people have come to accept that visual art must be representational, when that is not demanded of aural art, music.
There is a type of music that "ordinary" people like, ie music with lyrics ie songs, which could be said to be "representational".