In terms of a films' effects withstanding the tests of time, I think it's dangerous to think that a film from, say 1933, or even 1977 should hold up to a film from 2007.
I think that the way you experience a film changes over time. For example, audiences were completely sold on the reality of King Kong in 1933. In 2007, I can watch the film and appreciate it's cultural and historical significance. It doesn't take me out of the reality of the film, but the way I experience it is different.
Same goes for Star Wars. In 1977 I totally bought into the reality of the film. In 2007 I don't experience Star Wars in the same way - I appreciate it more for the nostalgic value than the actual worth of the film...if this makes any sense at all.