STArk,
You will get varying opinions on this based on numerous considerations.
1. Cost
2. Options wanted desired
3. Location
4. Financial Position
If you are buying the car with numerous option upgrades, it will be much tougher to find one without NAV. Most who bought or optioned Recaro Seats received the NAV (there are exceptions of course). This also holds true for the Sun Roof (again, there are exceptions). GOOGLE Maps will be tough to beat, but the Sync 3 NAV works well, especially if you have and intend to keep Serious XM, as I have. $700 for this option is a lot, but for me is well worth what I spent for it. Also, should be mentioned that Sync 3 NAV runs heads and shoulders above SYNC 2. So if your experience and others replying do not have experience with the 2 different versions, please keep this in mind.
Note:
Go on youtube and watch videos on how the system works to get a better understanding.
Best of Luck,