I don't particularly follow Bears logic of "if you want nav, you might as well add pro", as it's an extra grand on top, and however you cook it, you will lose money on it regardless of private sale or trade. It might make it slightly more desirable and an easier private sale, but for me, what you go for (nothing, standalone, basic or pro) comes down to three basic questions:
1. Do you need nav at all?
2. Do you want to avoid having wires trailing, and enjoy integration with the multicolour MFD?
3. Can you justify an extra grand to upgrade to pro nav?
It's almost pointless thinking about future returns. Just think about how much use you will get out of it yourself while you have the car.