I find the Nav system is more than just a screen with a pretty map on it. With all the electrical system settings and trip options that you can observe, I found it to be worth the additional cost.
2 Trip monitors with Elapsed Time, Driving Distance, Average Speed
Fuel Economy screen with Distance to empty.
You can set the engine oil and the tire rotation interval.
Tire pressure information / FLAT TIRE - low tire air pressure displayed on the screen.
Ability to change all the vehicle's electronic systems:
Adjust driver seat when exiting vehicle
Remote unlock driver's door first
Keyless remote response - horn
Keyless remote response - lights
Auto re-lock time
Sensitivity of automatic headlights
Automatic headlights off delay
Speed dependent wiper