Why hide?...if you're that good

The Gorillaz are a band that is never seen, only heard. Their music videos are an assortment of cartoon characters and anime which play instruments as representations of the band. Even their live performance at the MTV Video Music Awards left fans disappointed as 3-D imaging of the same cartoons from their videos was shown while the band played behind a black screen. What’s the difference between artists who are never seen and artist like Milli Vanilli which are the ‘face’ of some else’s voice? It seems as though the visual representation is more important, but does hiding your looks really deepen the significance of the music?