jasin,
I had an indash dvd in my old car and added GPS a few months after, got a good deal on the GPS.
I rarely used the GPS in my city, a few times when I visited some places downtown. If you drive your vehicle to other cities often, I would say it would be useful. I typically fly to and from most of my destinations, so I ended up in a rental car lost. I would weigh the cost of adding to how much traveling you do in your car.