I don't think a film and a TV show (which I'd not even heard about before now) establishes any kind of trend. A few years back, we had Buffy and Angel on TV, and that didn't spawn any broader vampire craze, despite a few sad imitator series. As for promise, I commented on 'Twilight' in another thread, suffice to say it was shallow and disappointing, and I expect the film to likewise be vapid. No idea what the show will be like; the fact that it's on HBO, and can theoretically produce a more 'adult' take on the supernatural, is intriguing, but at the same time being on a speciality channel can reduce it's penetration. For every Sopranos to come out of cable TV, there are several Carnivales that never catch on with the general public.
Fictitiously yours, Trent Roman