Is a work of art devalued by being overly reproduced?

Apparently the artist Jeremy Deller thinks so. Using normal everyday objects such as shopping bags, this artist comments on the present day ease of reproducing images. His untitled work of 2003 is a pink shopping bag with the statement, "Speak to the Earth, And it will Show You." (It is similar to the image above, a different work by Jeremy Deller).

I think he has a point. It is far too easy to reproduce an image in our contemporary culture. For instance, almost everyone I've encountered who has seen the Mona Lisa in person has been disappointed. Might this have something to do with the fact that Mona Lisa shows her face on t-shirts, greeting cards, playing cards and the like all over the world? There is something about such reproduction that devalues her appearance and the work of art itself. "Speak to the Earth (through your means of art) and it will show you." In fact, it will show you so much that your art will become a spectacle.

I still remember the red striped bar-be-que apron I saw with an image of the David on it for sale at a market outside the Galleria dell'Accademia in Florence. Tourists laughed at the sight of the naked sculpture on an apron. I guess I think it's kind of sad now. How can the world change our view of something simply by showing it's image over and over again. The media plays a specifically influential role in engraining images in our heads and skewing our perceptions.