you're touching on some interesting ideas about what art is. the economic half of your question can sort of be answered by the irrational behavior of the consumption of Veblen Goods[0]. the existential question has been addressed by a few artists, popularly by Richard Prince and less popularly (but more fascinatingly, imo) by folks like Elaine Sturtevant[1].

Contemporarily, artists like Clement Valla[2] are doing nifty things looking at the limits and our existing fascination with digital facsimile.

Here's an old essay http://en.wikipedia.org/wiki/The_Work_of_Art_in_the_Age_of_M... that asks some of these same questions (in particular the question of what would be missing). i think more interesting is the idea of what it means to own art and why we feel compelled to do it at all. Like they say: Everyone has their reasons.

this sort of question (which for me was triggered by Sturtevant) was hugely influential in getting me interested in fine art as a whole.

[0]: http://en.wikipedia.org/wiki/Veblen_good

[1]: http://en.wikipedia.org/wiki/Elaine_Sturtevant

[2]: http://clementvalla.com/work/wrapped-terracotta-neck-amphora...