I was debating the same thing. I have been using portable GPS units for years. I bought a new CR-V with NAV a couple months ago and decided that the built in NAV is worth it for me, so I am now shopping for a Ridgeline with NAV.
It is a good system. I have used many portables and this one works well. The voice tells you the streets.
Integrated with the stereo so you can have it so the volume mutes when the GPS is telling you something.
The NAV means I can use back up cameras with it on one large screen.
It includes voice navigation so I can tell it commands like "Fan Speed 4" or "Go Home" or "Get me coffee." Well, that last one does not work. But voice commands are cool.
The screen also has good information for time, stereo functions.
NAV means it is easy to spot icons for gas, food, stores.
Can be upgraded via a DVD from the dealer.
Does not block part of the windshield and use a dangling cord to plug in. Does not fall off the windshield.
The only downsides to me were initial costs, lack of bluetooth functionality, and of course you can't move it from car to car. I am also struggling a little, but I am sure it is me, with how to set it up to show me the things closest to me. And I would like a feature I don't think anyone has. Show me next gas stations, but in the direction I am going only. Not behind me.