A sense of style, or wearing costumes to be more theatrical, can be cool, but it should be about the music first. Bands often use those things to compensate for not having really good songs. I still like KISS, and I love that picture of that female tribute band (SLUTTER is a very clever name), but lets face it, they were a musically mediocre band that hit it big mostly because of their image and stage show. I feel the same way about 80s hair metal.
One of my favorite local bands, Takeover UK, wore their street clothes on stage, but they wrote amazing pop tunes, so I didn't care if they lacked a sense of style. Gregg Kostelich of the Cynics steals his wardrobe from Johnny Cash, but he makes it work for him, and Michael Kastelic always wears the same ensemble of jeans, sneakers, and t-shirts on stage. Gregg Prevost of the Chesterfield Kings has a great sense of style, but I mostly like the CKs because they are simply a great band with great songs. To me, style and costumes are only icing on the cake.