I think the general trend of the ABILITY of popular art to be influential in the long term is declining. In a barely literate European society, classical mythology and the Bible were the only things you could count on your audience knowing about if you wanted to use some stock character or allegory within your own tale. They ruled the cultural influence roost for thousands of years and nothing will ever match that from a longevity perspective.

Now not only is everyone literate, but literacy is, from a cultural perspective, increasingly unnecessary. Everyone has access to everything, and cultural works are now being targeted to microdemographics instead of even trying to appeal to everyone. Star Wars was before that last bit happened, but that last bit ensures there won't be another Star Wars. Or Beatles. In fact, I'd say Star Wars ranks pretty evenly with the Beatles.

The difference being, I doubt the Beatles would be nearly as popular today if people born in the 1980's and later could only listen to Wings and Plastic Ono Band, so long term, the cultural influence of Star Wars may decline faster than the Beatles.