I have an 04 Maxima and I got it with the in dash NAV system and find it indespensable. If nothing else, I can press two buttons and navigate myself home from anywhere. There are some nice advantages to having it built in. Lack of theft without taking the car is one. If they want the GPS, they can take the car too.

Regarding what kind of GPS would be needed, I don't think the decision factors are too broad. It's a vehicle, which drives on and off road, so why can't it have navigation maps and topos? With the memory costs these days it shouldn't be too difficult. I should probobly design one myself.

Let's be honest, of those of us to trek off the beaten path, we'd use handheld units which do have their limitations and require a fair amount of hands on interraction than what may be in an in-dash model does. To me, these are separate tools, like the differnce between a brad nailer and a framing nailer. You use the right tool for the job. you get the idea.