I would say it's more stupid to own a car that is rarely used. What a complete waste of money.
Too complicated to factor annual mileage in to road tax, although your insurance shoul be cheaper if you tell them you drive less than x miles per year.
If you do not use the car why not sell it? I think you should do that! Us road users are not called "Wallets on Wheels" for nothing. Alternatively you could organise a raffle where one of us ABers would win your car, and then both our problems would be solved. Good idea, eh?
I've always thought that road tax and insurance should be abolished and the cost lumped in with the price of fuel. This way you only pay for the mileage you do. More efficient cars cost less to run and insurance is underwritten by the government. Easy peasy.
But surely there is an argument to put the road tax onto the cost of fuel? The more you drive the more you're taxed (yes I know that happens anyway because of the fuel duty, but why can't they add, say, another 5p to the cost of a gallon and that represents the road tax).
I only do about 2000 miles a year in my car and an absolute maximum of 2000 on my bikes (I have 3 bikes (which I know is a little indulgent - although they are quite old) and on one of them last year did a grand total of 156 miles, yet had to tax it for a year because I don't know when I'm going to want to use it!)