"If the artwork turns you off from seeing the show, then I don't know what to say..."
Artwork plays a HUGE role in marketing a show. Yes, it IS a turn-off from seeing a show. Ask any of the clueless tourists (not the informed tourists). If you're a tourist wanting to see a show and are uninformed, you hear good things about a couple shows, and you pick up some brochures...are you more likely going to choose A LITTLE NIGHT MUSIC which looks very classical and shows a picture of a moon, or FINIAN'S RAINBOW which has stalks of rainbow streaks and a lone man standing on the vacant hills of a village?
Personally, I am in the dark on both shows. I don't know the admittedly don't know the scores (and am ashamed to say so), so in both instances my first exposure to the show is the artwork. Just by first appearances, I am MUCH more inclined to find out what FINIAN'S RAINBOW is about. Yes, if I do a little research I would discover that A LITTLE NIGHT MUSIC has a score by Sondheim and stars Lansbury and Zeta-Jones, and therefore may choose that show, but the artwork certainly doesn't assist in making the show interesting.
Poster art is vital to any show's marketing. The American Theatre Wing's WORKING IN THEATRE series once had a show devoted to marketing where they discuss poster art in depth. It's available for free on iTunes.
"The Spectacle has, indeed, an emotional attraction of its own, but, of all the parts, it is the least artistic, and connected least with the art of poetry. For the power of Tragedy, we may be sure, is felt even apart from representation and actors. Besides, the production of spectacular effects depends more on the art of the stage machinist than on that of the poet."
--Aristotle