Signals electronics (displays, sensors, etc) use so little energy compared to power electronics (the drivetrain system) that it doesn't really matter.
1 W * 1,000,000 cars is still 1 MW.
It's like saying a javascript file of 1MB is ok because there are images of 10MB on the same page.
A million of those cars is 200,000 MW
Amdahl's law: when optimizing performance, target the largest consumer first. And in this case the engine is the largest, by at least 5 orders of magnitude
It would save much more electricity educating people to drive less aggressively and use less braking than to remove the sensors