Valuable Art

I think there a few criteria that makes a piece of art valuable.
The most obvious is how aesthetic the piece of art work is. Such could be in the form of skill and technique in creating a lifelike realistic sculpture that of Mueck or like Pollock's abstract expressionist paintings. Their works are hard to replicate and their skills are easily appreciated.
Another thing that makes art valuable is the the message with which it is sending through the artwork. Powerful intentions and deep messages make an artwork a lot more meaningful as the content corresponds with the intended message. Such art will stimulate the audience to think beyond what is present in front of them, the usual things that are in your mind or present to you the obvious truth which is usually ignored. Such can be in a common form such as Hartini's effort to bring unity and less prejudice in her community. Or it could be as unconventional as Dadaism which even seeked to change the face of art as it was.
Of course once an artist's become famous, usually his artworks will valued. He or she would have achieved a level of respect for what he does which the general public can relate to. Often art which is original or has historical value will be valued very much. Another reason which may make a piece of art valuable is due to the cost which takes to make it. For instance, Hirst's diamond skull has a high value on its own before it was assembled. However, it is worth much much more afterwards.