I never realized just how bad a design this car was until seeing this video. The thing about raising and lowering the propeller drive never occurred to me as to just how dangerous and inconvenient that idea was.
The four wheel drive might be nice sometimes, but I've never been stuck with Amphicars two wheel drive. The closest I got to that was running up a long unused concrete ramp that was coated with moss. The tires on that car at that time had standard highway tread. I made it with a rather fast run at the ramp but I switched to tires with an all weather tread pattern after that and haven't had any slip since then.
One rather neat thing those old cars had was a self oiling system that would lube all the bearings from inside the car.