There's imagination, and there's imagination. I doubt novels will help you develop imagination the way e.g. solving spatial puzzles in your head will.

In my experience, prose doesn't force, or even encourage you to improve your imagination; it merely exercises your current levels. Kind of like opting for stairs instead of elevator when going up one floor - it doesn't really improve anything in your health, unless you're barely fit to walk, and is not a substitute for exercise that makes you reach the limits of your muscles.