I always felt one of the more suspenseful yet important elements of the show was Barnabas continuously having to hide his supernatural "secret" from Elizabeth. I'm proposing an unexplored subtext, but here goes:
Barnabas blamed himself for his mother's suicide (upon her discovery of his nocturnal hang-up in 1795), so perhaps in seeing Elizabeth's resemblance to Naomi, he subconsciously thought "Well, now it's 1967, and while she's not my mother, she's a dead ringer, and I vow not to repeat the same guilt, shame and tragedy with her - if I can avoid exposure in this century."
If the writers had allowed Elizabeth in on the secret of Barnabas, as they had Julia Hoffman, certainly Joan Bennett would have risen to the challenge. But then the ever-present dread of "Oh, wow, don't let Barnabas' entire family turn against him AGAIN when they learn the (gulp) truth" would have been compromised.
The premise as played out allowed us to fear for Liz (premature burial, werewolf attacks, possession by Leviathans), while still cheering for Barnabas to be loved and accepted by the family that let him down centuries before.