In regards to book covers, I'd like to share a story.
I attended an ASJA Conference one year and attended a seminar by a self publisher whose book got picked up and reprinted by Random House.
The whole book looked home made right down to the cover art and design. And yet, it sold copies. The book covered a nitch market for something to do with mothers with school children.
Random House put their resources behind the reprinting to bring the book up to their standards. Big difference from the self published version to the Random House version.
That is evidence the contents of a book is more important than the cover.