Now-- my understanding is that the "Frankenstein walk" originates in one of the movies where the monster is rendered blind and has to feel his way around — is that right?
Pretty much. The monster was rendered blind at the end of THE GHOST OF FRANKENSTEIN, so Lugosi played him that way in the next film, FRANKENSTEIN MEETS THE WOLFMAN.
Alas, all the dialogue relating to the monster being blind was cut from the final edit of the movie, so that the monster appears to be walking around clumsily with arms outstretched for no particular reason!
Glenn Strange (who played the monster in the next three films) seems to have carried this on for some reason.