True, this "middle class joe" doesn't have a porsche or a smart phone, nor am I interested in what data my car can provide. However my mechanic is interested and it would be neat if he could pull my car's diagnostics with an off the shelf device rather than have to pay the manufacturer thru the nose for proprietary equipment and certifications. My car even has a sticker behind the visor proudly boasting that only approved Mazda dealers can install upgrades for the car's software, for my safety of course, nothing to do with their after market sales figures...
Google are also interested in monetising my car's data but in a different way, the people who buy my data cannot link it to me, selling it to a third party has no direct/indirect impact on me other than dictating who pays for the adverts I see, it doesn't add to the cost of maintaining my car, in fact it could help to reduce servicing costs.
Data (information) has intrinsic value, it is the fuel that has driven the technological explosion over the last century, it can be traded for cash or used as a tool for 'good' or 'evil'. When everybody has access to it, technological and cultural progress goes into hyperdrive and everyone has a better chance of "keeping the bastards honest". When it is in the hands of a few, human nature dictates it will be used to extract/deny resources from/to those who don't have access.
Disclaimer: If I swapped my Mazda 6 'Sports model' for a real sports car, I would definitely want it to have a geeky performance display on the dash. If the car had an open API, it might even inspire my artistic side to write my own display layer.