When I was 10, I asked my parents for a set of weights. I had my Charles Atlas book to go along with that. Every time we went to the grocery store, I'd rush to the magazine area and read the ones with Arnold Schwarzenegger and all those guys on the covers: 'Pumping Iron,' 'Muscle and Fitness,' 'Muscle Builder by Joe Weider.'
No matter how beautiful and loved a cover may be, the jury on it remains uncommitted until the book has been in the world for a while. Perhaps bookstore buyers will be indifferent. Perhaps it will be lost on store shelves. Perhaps there's another book or two out there using the same or a similar photo.
I've mis-signed many a book Rollins or Clemens. My readers quickly become aware. Booksellers will often promote me under both names, and I do plug both at signings. Generally, the fantasy reader has no problem going into the suspense genre. It's harder for the typical suspense reader to go the other direction.