When you buy a car or sell your existing car do you prefer to be anonymous i don't think the concept of anonymity plays a very important role for mass adoption.. but since iota has privacy by default what are you worried about.. well yes most car drivers are not that bad so they don't mind to share details 
The point is, modern cars are already send data to car manufactures mostly without awareness of car owners. In every car where Android runs as a system (and that's already some) sends data. Have you ever wondered where the real-time traffic data comes from in Google Maps? In future, you will no longer be able to avoid such data collection, just as everyone already accepts it on their mobile phone today. The only question now is whether you prefer to get paid for the data or not.