Similar insurances in NZ, but it is only for the term of the first owner, so fine if you KEEP your car for 30 years it's going to be a nice new car, but as soon as you trade up you'll need a new policy for the new car.
The companies watch the statistics, which are a person/family in a position to buy a new car vs a used car generally keep it for between 3 and 5 years before trading up to another new car.
So they don't expect to replace many 12 year old cars... In the end the risks and statistics say it's not real different than the normal policy risks. It's unlikely to be the case of writing off an old $2000 beater and getting given the keys to a $40,000 new car, more likely writing off a $30,000 car and getting the keys to a $40,000 car.
I'd still just stick with Agreed Value policies. Write off the car and get an agreed amount of cash. Simple check, "is it fixable? Yes, Fix it, No, Here's your cash. No arguing about the fact the "equivalent" car is a different colour, automatic instead of your manual, single CD instead of 5 disc changer... or the cash the want to give you under the replacement value policy is for a bone stock blue booker value, not your slammed, chromed, bagged, 30" wheelied Stancemobile with a custom paint job...
Seen it all happen before, much easier having a simple, agreed amount of cold hard cash handed over. Just up the policy value each time you bolt on another breakable, expensive, go-faster piece of bling.