Worth noting that without the service plan if you are on a trip and there is a problem, Road Side Assistance will come get the car for service if it prevents the vehicle from operating properly/safely.
The annual checkup discount available through the plan may be useful, but there isn't that much to service-- no oil change, no transmission, brakes should only see light use, no serpentine belt, etc.. If you miss the annual, and get a service in 18 months or so, you may be better buying a la carte annual checkups.
The Ranger service is really useful for folks who live far >45 miles or so from a service center as I understand it... so they can get warranty non-critical things fixed easily.