In the case of electric cars, the state and federal incentives that help to make them attractive are available only when they are "new".
Ahh yes, they must benefit the environment only when new :)
Given the increased prices in the used car market (arising in part due to better durability and quality), I think I might be able to make an interesting argument for incentives towards purchasing used cars as being better for the environment than incentives for purchasing brand-new electric cars.
I think in the US we would get the most mileage out of reforming CAFE to make it less friendly to daily driver trucks.