I wonder if anyone's discussed the issue of anecdotes about customs which actually hint, by their details, to significant issues, but the significance is since forgotten, at least in the vulgar versions? I can think of two examples:
1. The tale of the rebbe who cut his fingernails after the mikva. His Chassidim thought it was imbued with significance and wanted to imitate him, until he pointed out to him that his nails are softer and easier to cut after the mikva. In the retellings of this story, the issue of fingernails as a resting spot for ruach ra is not noted. Whether or not such a story is true, surely the issue of whether to cut the nails before or after the purifying agent of the mikva is of some concern to mikva going rebbes.
2. Someone told me the following joke he heard from a leading rosh yeshiva of an earlier generation (its context was the issue of ecumenism in the early '60s): A priest, a minister and a rabbi decide that in the spirit of tolerance and the times, each ought to modify tenets of their religion to bring all men closer together. So the priest says "Well, we'd be willing to do away with Immaculate Conception." The minister says "We'd be willing to do away with the Trinity." The rabbi says "We'd be willing to get rid of the second yequm purkan." This joke almost turns its grain of historical basis on its head. If I understand the joke correctly, the rosh yeshiva meant to say that for Judaism even the least practice is as significant as the chief dogmas of the other religions; ecumenism is pointless. The issue of removing the second yequm purkan (or the whole thing) was a topic in 19th century Reform, and especially in Orthodox polemics about Reform.