Cecil should be aware that the interpretation of “The Wizard of Oz” as a parable on the gold standard has entered widespread acceptance within economic circles. Hugh Rockoff published “The ‘Wizard of Oz’ as a Monetary Allegory” in the Journal of Political Economy (98(1990):739-760) laying out the details of how a bimetallic monetary policy would reduce deflation and, in Baum’s mind, cure America’s ills. N. Gregory Mankiw, a later chairman of the Council of Economic advisors, published a summary of Rockoff’s work in his intermediate macroeconomics textbook in the early 1990’s and the book later became the discipline’s standard. The story livened up some otherwise drowsy models.
The column in question is Is The Wizard of Oz a satire of the French Revolution?
The update that Cecil added is pretty much a direct repudiation of Littlefield’s thesis. You need to read both to see which is more believable to you, although Parker’s article is a summary of the opinion of actual historians.
It’s not impossible that some allegory is present. But Baum was a hack writer who ground out dozens and dozens of children’s books under a variety of pseudonyms. Authors who do that aren’t normally creating political satires. They’re just worrying about getting the words on paper.
It may be true that economists still want to believe. But it’s also true that all the writers who do books on how Shakespeare didn’t write Shakespeare are not English professors. In other words, though the theory has a long history and was around way before Rockoff, I wouldn’t put any money on what economists have to say about authorial analysis.
He didn’t just write children’s books; he also wrote teenage adventure books and adult thrillers, not to mention a book about raising chickens and many magazine articles about shop-window decorating. (In fact, he is regarded as the founder of window decoration as a profession.) He wrote plays, too, and musicals, and silent movies (which he also produced).
I have a friend who is a leading Baum expert and has virtually all his books. You might say I’ve seen more Baum than I care about knowing. 
I still say he was a hack. Of course, I say that Conan Doyle was a hack, which is not the majority opinion. They both could write but mostly ground out sausage. I wouldn’t look at Doyle for political allegory either. Milton, yes. Every line had an allegorical meaning. But Baum? Highly unlikely.
My old high-school history textbook had a boxed text detailing Littlefield’s populist/monetary thesis as fact. Stupid Texas textbooks.
Baum (and Conan Doyle) were gifted hacks.
(If you have a friend who’s a leading Baum expert, he probably knows me. I have virtually all his books, too.)