Dante, I'm a professional artist with 25 years of experience and 4 years of college, and I already know not to design my covers. I'm too emotionally close to the work, and I need to turn it over to some savvy marketing people. My publisher worked with me to get a good compromise that seems to do well as a thumbnail. When I had some reservations about a cover element, they changed it.
Please, please take this as a well-meant critique from someone who has been in the trenches: do not make cover art your only yardstick for accepting a publisher offer. The numbers of artists/writers who can actually design an *effective* cover are very few, as opposed to the ones who think they can.
By broadcasting this philosophy - especially to publishers or agents through your query letters, you are giving them one more reason to say 'no'. They don't know how good you are, or how much experience you have in art marketing. But they will possibly get the idea that you might be 'difficult' to work with, and go with someone who might be easier.
I could show you a self-made cover here on AW that went on to be used by a professional publisher, because (I suspect) the art department manager didn't want to fight with the artist-writer. The cover was so unprofessional it almost turned me off that publisher. I won't, because my heart aches for the author, who doesn't need any more problems.
I can also point to the work of a fantasy writer/artist named Janny Wurts, whose artwork is technically as good as nearly anything out there - and it still doesn't help her books.