In this adventure, Herbie not only goes to the Devil, he meets Liz Taylor as Cleopatra as well. Cleopatra turned up in a number of comics in this period because of the Liz Taylor movie.
Frankenstien and Dracula were recurring characters at the American Comics Group. The original characters came from fiction and were in public domain, but the versions used in Universal horror movies were ( and are ) under copyright, so the ones used here could not resemble the movie versions too closely.
Here we see a complaint about something in a Herbie story being impossible. But in the world of fantasy the impossible may be allowed.
Another letter complains about formula stories. But a lot of fiction is done according to formula, Leonard Maltin's criticism of Terrytoons notwithstanding.