As MB and others have said, this movie is just another version of Dark Shadows that some will like and others will not. It doesn't in any way prevent anybody from enjoying any of the previous incarnations, much like Abraham Lincoln's appearance in Abraham Lincoln, Vampire Hunter (or, for that matter, Abraham Lincoln's "appearance" in Bill and Ted's Excellent Adventure) don't change the legacy of his presidency.
For better or worse, I think the vast majority of our fandom have already made up their minds about whether they're enthusiastic about this movie or not, and based on everything I've read there isn't anything that's going to be done or said that's going to change many minds. Those who are unhappy continue to find things that make them unhappy. Those who are gung ho are not going to be dissuaded. Similarly, those who are looking forward to the movie continue to point to things that they think are positive, but they are not likely to change the opinions of the former.
As for the latest points (and I'll put them all in spoiler tags just in case some view them as spoilers):
[spoiler]If the "character" in question is the werewolf eluded to, it's still a fairly large leap to assume that's Quentin (or Chris). In one of the trailers they have a werewolf in the Scooby Doo episode they're watching.
As far as the David line, I'm not as dismayed as others are about this. In Forest Gump, the preadolescent Forest mimics the funny sounds the doctor made when he was sleeping with Forest's mom in order to pay for his leg braces. Kids don't necessarily understand the context. I didn't find that disturbing, while I did find the scene with the crucifix of a similarly aged Reagan in The Exorcist much more disturbing. I have to at least wait to see the scene before I can get all that worked up about it.
Finally, I presume the objectionable scene is the one of Julia performing oral sex on Barnabas. While FAR more graphic than anything that could have been shown on daytime television when the original series aired, didn't a fair portion of the fandom want Barnabas and Julia to end up together? It sure seemed like Julia had an unrequited love for Barnabas. While in the original series they could not show her engage in such an act, it's not really so far fetched. In the latest Mad Men, they showed a very similar scene that ostensibly takes place in 1966. [/spoiler]