For me, I will to some extent be influenced by the cover, it does make a difference when buying or even browsing for books. If i see some dull boring cover with just one or two words on it and no clue as to what its about, I probably would give it a miss, even if the story was good. On the other hand an eye catching cover, particularly with horror or mystery, would grab my attention and if the author makes a decent effort with the cover, its the icing on the cake if the book turns out to be any good.
I also think its handy when books put the film stars of the book (when adapted) on the cover as I had no idea The Woman in Black was a book until i saw Mr Harry Potter on the cover, similar with The Road and The Town, it helps the book reach a new audience.
You only live once.....so live!