ACC is a complusory insurance scheme. Levies are analagous to premiums and should be proportional to risk, where possible. The question IMO is how do you fairly assess that risk? I would have thought ANCAP rating or similar would be a good enough proxy. Yes people on lower incomes will pay more if they have older cars, but they are posing more of a risk. ACC isn't a tax system and therefore doesn't need to be 'progressive'. Life isn't always fair. I pay higher insurance premiums and /or have reduced cover (life, travel and health) because of very generous decision I made to help someone else.
I also don't understand why we allow new cars to be registered that don't have air-bags, ABS and stability control. So what if they are commercial vehicles? Surely we want people to be safe at work?
Also, a big chunk of the new vehicles sold in NZ are commercial vehicles and they are the future used vehicles. It makes sense to apply decent safety standards to these vehicles.