I too am of an age to have watched DS when originally aired--but have zero objection to attracting the teen audience. I would mind if that were the only audience targeted--just as I think a film intended solely for fans of the first series would be...well, hopeless. I want new fans for Dark Shadows! Lots of em! I want the DS Festival to swell in size, to branch out and need to meet on both coasts each year!
To do that, IMHO, requires a good movie. Not one that simply retreads the same details and essentials as before, but a fresh and compelling take springing out of a good script, fine performances, good direction and design, etc. Trying to manipulate an audience into liking something very rarely works. What is needed is for the filmmakers to all be on the game, on the same page, and making a movie they'd want to go see! As ever, it'll be a crapshoot. Plenty of wonderful flicks never found an audience for a variety of reasons (mostly coming down to blind luck).
But let us also not forget this movie is a movie, not a soap opera of twenty-five minutes each day for several months. It may be set in 1971, but will be shown in movie theaters in 2012 for audience members who have a somewhat different sensibility. That fact is no more "good" nor "bad" than the existence of CGI or of color.
Bottom line: I'm hoping for a good movie, for myself and others, including those who've never heard of DS before now.