Actually they smiled a lot in the show, particularly John Astin with that wide-eyed borderline-maniac grin. The cool thing about The Addams Family was how deliriously happy the Addamses were with themselves. As far as they were concerned, they had the ideal life and it was the rest of us who were the neurotic weirdos. Quite a subversive statement for the day.
I guess. It was subversive the first few times, but they did it ad nausem, and after a while it lost all impact. A clever show overall to be sure, tho.