Good questions !
Frankly speaking I do not see much of a work of art in those pieces of wood but this exact questions came to my mind many time so far when visiting museums. A lot of work of art did not seemed to be as being really that great but I always thought that I need more education into art to understand some of the paintings and objects that were so much appreciated by others. Going further for example, the wood frame, painted and with 2 paint stained rubber shoes nailed seems quite expressive to me and this looks really as a piece of valuable work of art. Anyway, what I think is that the value of a piece of art is given by the specialists in relation not only to its look and appearance, but also in relation to the artists reputation and career. Having that said, I think there are a few more other things that are considered and we might not know about them, like for instance the size of artist's market and his overall quality.
Art is way much complicated than we can imagine, and sometimes maybe only some of us have the gifts to understand it. In any case, this was a great article and I am going to follow you for more. Keep them coming !