Thinking out loud again. It seems to me the only way you can get deflation is through hoarding. Even money kept in banks is invested, since they have to invest to stay in business. Of course, if they loan the money, and it is lost, then it is gone, too. You have, say, a house that has been built, and the workers and suppliers paid. You lose, there, the excess the bank expected to make, resulting in the loss of the bank. Yet, the excess was retained by those who were paid, so the money is still there.
But if you put money in a mattress, it is out of circulation. This causes a decrease in money, which causes a decrease in prices, which over time causes a decrease in inventories, and an eventual loss of jobs.
In trying to figure out the Depression, you have to figure out where the money went. There may be a simple answer to this. One obvious answer is that the high tax rates Roosevelt charged on investment income, and on income for the rich in general, caused them to in effect put the money in mattresses.
If you have money, though, you also get good deals in deflationary times, so it would be worth finding out who, if anyone, benefited from the Depression, other than the Statist Democrats. What wealth transfer happened, if it did? Perhaps one could argue that wealth was transferred, permanently, from the private sector to the government.