We hate to break it to all you folks out there hoping to dress as Gloria Swanson at the next cosplay convention, but Sunset Boulevard doesn't have the kind of cult following that Star Wars and Indiana Jones do. Being a satire on Hollywood, it's just not that kind of movie.
But it's definitely popular—as evidenced by its inclusion on major award lists—and has had a pretty serious influence on the history of movies. Anything that's self-referential about Hollywood probably owes some kind of debt to Sunset Boulevard (like David Lynch's Mulholland Drive, which even has a famous L.A. street as its title), along with certain movies that are skeptical about the American Dream (like American Beauty). It might not be selling a ton of swag like the Harry Potter movies, but it makes up for it by being an essential masterpiece that film buffs the world over have studied and studied again.