I've been thinking a little more on this. I'm strongly put off by anything that seems to be romance lit and cover art that bodes ill in that it's-a-romance-book way wouldn't attract me. On the other hand, I like good illustration a great deal, on the cover or on the inside. A year or more ago when I was talking about a book that Fbaezer recommended, Agustin Yanez's The Edge of the Storm, I know I rattled on about the woodcut illustrations as much as about how I was taken by the writing. Good package - good writing, illustrations I liked. Still, my favorite books often don't have either cover art or illustrations.
I keep an old paperback book on bread by James Beard not so much for the recipes but for his own drawings.
One thing I've stopped doing re police procedurals is reading either the blurbs in the front of the book or much past the first line of any blurb on the back. I like discovering content myself and not being blurb fed what is about to happen, even if it is just the start of the storyline. But - I tend to choose procedurals for either the author if I know his or her work, or the setting, so it would be a way for me to at least learn about a new city or country other than my own if I ended up not liking the writing.