Well, come to find out, it's a parable about monetary standards, at least on this fellow's reading, who claims it's all about William Jennings Bryan and the fixed indexation of silver.
To reach the Emerald City she must follow the Yellow Brick Road, which can be safely traversed only with the magical silver slippers (gold and silver must be in proper parity). Dorothy is protected by an indelible kiss from the Good Witch of the North (an electoral mandate.)
On the yellow brick road, surely one of the most dangerous routes in American literature, Dorothy encounters the silverite constituents. First, the ridiculous stuffed Scarecrow (the farmer), who cannot scare anyone and who fears he has no brains. Actually his behaviour shows him to be highly imaginative and responsible (so much for the ridicule of the hayseed in big-city newspapers).
The travellers then encounter a vivid symbol of the oppressed industrial worker, the Tin Woodsman. The Wicked Witch of the East had cast a spell so that every time he swung his axe he chopped off part of his body. He is entirely tin now, a purely mechanical being who fears he has lost the power to love. Alone he's helpless -- he can't oil his joints -- but in teamwork he proves effective and compassionate. (The industrial workers, dehumanized by industrialization, need to become aware of their latent compassion, and co-operate in a farmer-labour coalition.)
Finally they encounter the Cowardly Lion, who does frighten people but who says he lacks the courage to do his duty. Working together the coalition fights its way to the citadel of power, the Emerald City (the national capital). The Wizard, of course, is a charlatan who tricks people into believing he wields immense power; even his Emerald City is only an optical illusion. (emerald-green paper money is likewise a delusion.)
Damned Hollywood! Turning the silver slippers to ruby ruined the whole thing. I mean, if you're buying. Curtsy: Creative Minority Report.
Update: Chris left a must-read "rest of the story" in comments. Lege.
