Here's your retirement project, John. Invent a Heads-Up Display that will work with 3D GPS. Just use the windshield as the screen. You could also incorporate a radar detector display, HamHUD, stereo controls, etc...
But, I will swallow my pride and agree with Jack on this idea. Although the in-dash units are neat, I've never been a real fan. The only reasonable benefit I see with those types of units is the ability to get directions. You can do the same thing with a map, and you've saved $2000.00.
With the in-dash units, your options are too limited. The device cannot be taken out and used off the trail when hiking, exploring, or utilized in any Geocaching events. Also, downloading routes you've traveled to a computer to print maps, share with others, etc., becomes complicated.
IMO, the laptop just kills several birds with one stone. OBD-2 software, storage for pictures, RAVE Manuel accessibility, GPS, etc, etc, etc.... the list goes on forever. These days, it seems like a laptop is about as valuable as a cell phone - how many people leave their home area without a cell phone or laptop? I know you probably have a concern with mounting a Jotto or RAM mount to your vehicle, and then the hassle of dealing with the computer..... But, once it's there, it really is convenient.
I guess it's all in what you want. It's a lot of money for those in-dash devices. I just feel in the long run, it's not going to be something to write home to mom about. And, it's a little too "Honda Ricer wannabe" for a Rover - especially a Defender.