Again, this assumes this is the only input, and things can't detect when some inputs seem completely insane with high probability and raise an error

Seriously. Y'all realize how much in your daily life would pretty much explode and kill people if that wasn't true, right?

It's worth mentioning that car GPS navigation explicitly calculates how plausible each GPS reading is, based on a combination of other position signals and basic physics modeling, and discounts anything that sounds too crazy. If it didn't, simple things like tall buildings would be huge problems.

Tall buildings are huge problems for GPS. Multipath reflections will inflate the uncertainty and can put you some distance from your true location.

Yes, they're a serious problem. What I'm saying is that they'd be a much bigger problem for GPS-based car navigation if there weren't logic in place to combine the GPS info with accelerometers and gyroscopes.

Yeah, but that wasn't my point.. my point is that these attacks will be tried as soon as opportunity>cost-to-attempt