Personally, I'm a fan of taxing usage (and not the car itself). As said already, if you're paying €100k+ for a car, you're already handing over a big wedge in VRT & VAT.

The only realistic way of doing this is abolishing motortax (or at least vastly reduce the rates) and increase fuel taxes, so the more you use, the more you pay. It's the only fair system really (yes I know it would hammer rural people more than city dwellers). At least you would have the option of not using the car and it would encourage car sharing, bus, Luas, walking, cycling, whatever.
At least you can have a car for weekend duties without having to pay for its large periods of non-use.

Why should I have to pay totally unethical motortax rates on a 3 litre petrol that will only do 5k miles a year versus someone in a 1.6 diesel Passat (paying less than €200 pa) but doing 30,000 miles a year ? Morally & ethically wrong !