Changing a Tire (d) Cover
Several months ago, one of the Smashwords authors who had been selling steadily but poorly paid up for a new cover. Immediately thereafter she began hitting the best-seller lists for indies. My memory doesn't serve me well enough to name the book or even the genre (romance or erotica is my recollection), but her author interview supported all of the above remarks.
That said, no one should be too timid to try something a bit different. Our own Hugh Howey with his Wool series has proven that creativity does not end when we write finis. Hugh, if you read this post, let me once again offer a tip of the hat for a job well done--this time for your instinct in stepping outside the norm of look-alike sci-fi covers.