I do think you have a point. If an actor I think is a good talent is acting in a film, then it's more likely that I'll end up watching it. It's not that I fancy the actor or such, it's just that I have enjoyed the acting by the actor in the past, so that even if they're in some mediocre film, they're likely to still add to it in their own way and give me an added interest.
Still, yeah, if you just watch a film simply due to fancying an actor, then that's pretty shallow on its own. However, to watch a film because an actor whose acting you've respected in the past is in it, then that's a different reason in my book.
Anything with Edward Norton, Al Pacino, Cary Grant, Helena Bonham Carter, Cate Blanchett, Lauren Bacall, Katherine Hepburn, Spencer Tracy, Susan Sarandon, Harvey Keitel, Tim Roth, Steve Buscemi and a few others will pique my interest in the film.