I've got the nav system in my EL and like it just for the sake of convenience. I had a laptop mount in my Excursion and ran topo software on my laptop for when I was off-roading... and would probably still have to run it just because the nav system doesnt have anywhere near that kind of detail. If you go off road with the nav system, you're just in a black hole on the screen.

Radio-wise, its nothing great. If you're wanting a premium system with crystal clear sound, you might be looking to upgrade if you go the nav radio. Dont get me wrong -- its better sound than the radio/speakers in the Excursion but I dont know how much of a music snob you might be.

An aftermarket GPS might give you more options in terms of what you can do with it. There are some features that I miss on the nav system, like an altitude and speed display, and the ability to put in coordinates as a destination. However, the nav system has features that my topo software doesnt, like the ability to just punch in a name (like Camping World) or a telephone number to come up with an address -- then you just set it as a destination and away you go.

I think for the typical on-road driver, the nav system is about all anybody would ever need. As I said, its very convenient to have it right there all the time with no extra mounts/wires, etc.

As for whether its worth the extra $$$... thats probably a matter of perspective. If you dont mind a windshield or dash mounted aftermarket GPS, a VERY nice one can be had for less than half the money and will do pretty much the same things.

I've got a Garmin in my Super Duty and feature-wise its very similar to the system in the EL (though I do like the larger screen on the nav system).

Dont know whether or not that helped, but maybe its at least a little more food for thought.