The built-in navigation system does not require a dealer visit to update. You can purchase map updates here:
https://infiniti.navigation.com/product ... nitiNA/USD
They come as a set of five DVDs - the first DVD updates the firmware of the navigation system, and the remaining four DVDs update the maps.
Installing the maps requires a license key, which is really what you are buying for your $149. At the time of purchase, you provide the navigation vendor with your Nav Unit ID, and they generate a unique license key for your Unit ID that allows you to install a certain year's maps. After the firmware update and as you begin the four-DVD map update, the nav system will prompt you for the license key.
I did this myself a couple of weeks ago. There are a few threads here in the forum on the topic, but the biggest issue is that the process takes a long time, and the power to the car shouldn't be interrupted during that time. I used a high end battery charger to provide power to my car while it updated, which I highly recommend vs. letting your car idle for 2+ hours.