I've only recently started Prince of Wolves, so forgive my ignorance.
1. I'd actually like to see less of the game mechanics specifically called out in the books. Yes, the books need to stay true to said mechanics because those are the rules of the world in which the books are set, but they don't need to be described as such. Also, I'm new to PF and don't know much about the campaign world so some of the references in the book are over my head. And there's a section where Varian is doing research and comes across bat guano. He mentions it's a spell component but offers no further information. I knew what it meant, but someone who is new to the books may know nothing about the game or world. I think this might actually keep new readers away as they might feel thrown into the middle of this world they know nothing about. I know some die-hards might not like this, but we're already playing the game, reading the books, and posting on the messageboards. We usually want what we think we want and that may not be what helps the book line grow.
2. & 3. I love the paperback covers for Raymond Feist's Riftwar Saga. Bright, bold colors with simple artwork. Grabbed my attention right away.
4. Not sure I can help here.
5. Take this with a grain of salt because I play the game and love to paint minis, but what about a Reaper Mini/Pathfinder Tales tie-in? It would intrigue me to pick up a novel packaged with a couple of appropriate miniatures I can paint and I'd be willing to pay a premium for it. Of course this only appeals to FLGS customers.