allfoak
Alchemist
I am familiar with this interpretation.Actually, the yellow brick road is a metaphor for the gold standard, which leads to the Emerald City (paper money - green, since it's American), where everything looks impressive but is just a hollow facade run by the Wizard of Oz (oz... as in ounces of gold), who himself turns out to be a fraud.
Dorothy - who represents the American common people - is eventually saved by her silver shoes (changed to ruby slippers for the movie), representing a changed to a mixed gold/silver standard, after having met along the way the scarecrow (the American farmers), the tin man (the American manufacturing workers) and the cowardly lion (William Jennings Bryant).
I can't remember who the witches are supposed to represent, but they're allegories to 1890s American politics, too.
It is the genius of the movie that it can be understood in so many different ways.