Dracula '31 and movies like House of Dracula-- tend to be earnest nightmares that have a sense of innocence about them-- at least those coming from Universal. These movies could be watched by children today with a few exceptions. Everything is clear and unambiguous. Dracula is a monster, and if he offers any temptation to the dark side, it's an understated temptation.
In the Gothic Era of the 50s through the early 70s, from Horror of Dracula to Vampire Circus, you get a more complicated moral universe-- here, the vampires are enticing and the get more beautiful; Christopher Lee is attractive and the Brides tend to be pretty hot. The idea here is that evil is attractive, but the movies still remain firm in the notion that the vampires are evil. This gets really complicated in movies like Vampire Lovers, where evil must be punished but sure seems a lot more rewarding than everyday morality.
In the modern era, that clarity is gone-- in movies like Interview with the Vampire, Queen of the Damned and certainly Twilight, vampires are either an alternative lifestyle or an alternative race existing symbiotically with humans.
I think all of these theories have their place. Sometimes I want to watch the child-like fantasies of the Universal horrors. But I find the middle period the most fascinating, because there's a genuine conflict there: the movies hold out a universe where the forbidden is genuinely enticing-- but to do the thing that is most enticing, to dally with vampires, is to tempt the wrath of God. In the modern movies, the wrath of God is no longer a concern. There is only loneliness, and with any luck, love. There is no more temptation because there is no more forbidden.
What seems strange to me is that the belief systems of the audience can't possibly be the reason for this shift. The moral universe of a movie about magical beings has nothing really to do with the moral universe of the audience-- that is, it doesn't matter if you or I believe in Heaven or Hell to follow and get involved in a movie that believes in Heaven and Hell. But the threatened loss of a character's soul makes for much greater conflict. More likely it's a cycle: we are in the era of vampire romance, and the concern for the characters is a concern for their happiness and not their salvation.
All of which is funny when you consider what I write are adventure books where the vampires are on the evil side. So there's no temptation there to begin with (not in the first couple of books.) But I think if there were, I'd make it a dreadful worry.