Last night, I was reading Brian Leiter's introduction to his edited volume, The Future for Philosophy (Oxford, 2004). In his description of "Wittgensteinian quietism," he says that philosophers in this vein have turned to the "history of philosophy, which shows us how we came to think there were such things as philosophical problems and philosophical methods in the first place." (p.2) In the footnote to this statement, Leiter writes: "An influential, but little-published, Harvard philosopher, the late Burton Dreben, purportedly gave hyperbolic expression to this Wittgensteinian view in an oft-repeated line: 'Philosophy is garbage. But the history of garbage is scholarship.'" (n.7).
I stopped reading and wondered whether Professor Leiter had ever heard the story about Gershom Scholem lecturing in New York. The story goes that Saul Lieberman, a professor at the Jewish Theological Seminary and one of the leading Talmud scholars of the day, introduced Scholem's lecture by saying: "Nonsense is nonesense, but the history of nonsense is scholarship." I also wondered whether Burton Dreben had ever heard this story.
A quick Google search for "Dreben Scholem" led me here and an answer to my first question. One of the commentators to this post about Dreben on Leiter's blog (written after he had published this introduction) points out that Dreben had been married to the daughter of another professor at JTS, Shalom Spiegel.
This also probably answers my second question. It seems probable that Dreben heard the story and the pithy formulation from his father-in-law, admired the turn of phrase, and recycled it in relation to his own subject. It should also be noted that in his 1941 Major Trends in Jewish Mysticism, Scholem thanks Shalom Spiegel, then of the Jewish Institute of Religion, "for his unfailing friendship and readiness to give of his time and help."