I have not seem evidence that the cell phone boosters work. They would need to act as a ground plane to do so.

The Antenna on the N810 is part of the upper backplate. The section above the battery cover.

If you remove this it connects to bads on the circuit board.

Theoretically you could be able to make a cover that replaces the antenna with an N connector allowing you to attach a external antenna.

The main advantage of this would be that you can place the antenna outside the car.

While you could put a higher gain antenna in. This would not help much with GPS. Antenna gain is archived at the price of making it more directional.

As this antenna needs to pick up 12 satellites in different directions. You are limited in how much gain you can add. But a little is possible.
PS a GPS works on 1227.6 MHz and 1575.42 MHz Cell phones are at 850 / 900 / 1800 / 1900 MHz depending on where you are world wide.