The utilitarian argument for them is very strong.

Doubtless a national numberplate recognition system would be effective at enforcing the speed limit.

Once we have it, it would also be of great utility to investigate kidnappings and terrorism. And serious and violent crime. And vehicle thefts. And drug trafficking. And driving without a license, insurance, or tax. And lying about your address to get your kid into a good school.

And who could object, when we're already storing proof of what really happened, to that proof being used to vindicate the innocent in a divorce hearing, or an employment tribunal?

As faithful believers in the free market, what better way to fight congestion and encourage the use of public transport than a tax that only applies on congested roads, and only at peak hours of the day? What luck, the infrastructure is already in place.

No doubt the system will be expensive to design and operate. It would help defray the costs if we release citizens' travel records to some carefully vetted partners, such as academic researchers, urban planning consultants, insurance companies, marketing companies and credit rating agencies.

We already have numberplate recognition and its essentially on a national scale, just not completely linked up from jurisdiction to jurisdiction. License plate scanners are becoming rampant in some areas, they apparently have never been successfully blocked, all for reasons you listed and also as "license plates and vehicles don't have rights". The favored method for abusing a person's rights is to target their things

Perhaps I can incorporate my car, and get it some rights!

Do you have evidence to back up that claim? It seems counterintuitive that slowing down the top few percent fastest drivers would improve traffic. If there's enough traffic to cause congestion wouldn't they be stuck behind slower drivers anyway?

As you go faster, your stopping distance (that is, the distance you should maintain between you and cars in front and behind you) increases. This leads to roads having a maximum capacity somewhere in the area that speed limits are set. If you go faster than that, you're reducing efficiency of traffic.

Anecdotal evidence, but it also makes intuitive sense if you consider that vehicles travelling at a range of speeds and particularly changing lanes to overtake the slower drivers is effectively a turbulent flow. If that flow can be smoothed, as a body it travels faster.

I know the trucking industry regularly criticizes the safety implications of having a separate speed limit for them, as it makes lane changes much more complicated. They aren't impartial to the financial impact of the speed limit though, so there's that.