I Am Not Spock: Averted. Al Lewis loved his Grandpa Munster character, and eagerly exploited it.
Played more or less straight with Fred Gwynne, who spent some years distancing himself from Herman until he was given a sweetheart deal to be in the 1981 TV movie The Munsters' Revenge.
Keep Circulating the Tapes: The 1973 animated special The Mini-Munsters, the television movie Here Come the Munsters, and the revival series The Munsters Today.
Money, Dear Boy: Yvonne de Carlo really did not care for the show. She only took the job because her husband (a stuntman) was badly injure, and they had exhausted most of their savings on medical bills.
The Other Darrin: Beverly Owen played Marilyn in the first 13 episodes. After she left to marry Sesame Street writer-producer-director Jon Stone, Pat Priest took over for the rest of the series.
Later still, Debbie Watson then took on the role for the following movie, Munster, Go Home!
The Pete Best: Marilyn was originally played by Beverly Owen, but only for the first two-and-a-half months the series was on. When she left the series, Pat Priest took over the role.
What Could Have Been: Fred Gwynne was offered to reprise his role as Herman in The Munsters Today, but he declined. In an interesting inverse, Al Lewis offered eagerly to reprise his role as Grandpa, but he was turned down in favor of Howard Morton.