P. D. Q. Bach routines contain a certain amount, tends to age quickly. But P. D. Q. Bach continues to go his merry way, with his motley collection of instruments at the ready, his dill piccolo and his shower hose among them, and people keep paying good money to hear them. Schickele has even tried to retire P. D. Q. Bach in order to promote his own light music, but the composer of the Fanfare for the Common Cold has been brought back by popular demand (and according to his website, because he needs the money).
What's the secret? Why hasn't this essentially one-joke routine gotten old? The answer is that Schickele has the whole history of classical music for his bag of tricks, his comic canvas. The heart of Schickele's act consists not of jokes about a fictional Bach offspring but of actual music music that parodies styles far beyond the Baroque era during which J. S. Bach and his sons lived. By now, the list of P. D. Q. Bach's "works" runs to thirteen pages, so you can see Schickele several times and not repeat the same material.