[joshvm]

Others have commented about the human aspect.

> Two cameras of any resolution spaced a regular distance apart should be able to build a better parallax 3D model than any one camera alone.

This is true if the platform isn't moving.

If you have the time dimension and you have good knowledge of motion between frames (difficult), you can use the two views as a virtual stereo pair. This is called monocular visual/inertial-SLAM. You can supplement with GPS, 2D lidar, odometry and IMU to probabalistically fuse everything together. There have been some nice results published over the years.

But in general yes, you'll always be better off if you have a proper stereo pair with a camera either side of the car.