Jeremy Olson, while in the midst of an iOS 7-friendly redesign of his app, Hours, has written down some great points about redesigning an app for iOS 7:
Winning apps won’t merely take Apple’s default look and mimic it. Think about how boring it would be if all of our apps looked like iOS 7 Calendar or Settings. It would get old really fast. But that’s nothing new. Think about if all the apps on iOS 6 looked like iOS 6 Calendar and settings… Yep, it would be really boring.