Two quibbles: first, "households with PV" are still not mainstream, even counting utility-installed grid tied setups*. You'd be better off just arguing "reduced fuel and maintenance costs." Second, the decision to buy a new car is not, for the vast majority of people, math-based. They will try to decide if they can afford the payments - on a car they've already decided, for decidedly non mathematical reasons, that they want.New vehicle average prices in the USA are approaching $40k. The $10k difference that you emphasize is easily covered by fuel costs differences for households with PV even if no tax credits are available. I'm presuming that 10% of the USA households can still do arithmetic.
* Searching briefly for a number or percentage, I'm not sure that anyone has one. The common approach is to look at installed solar capacity (an estimate, apparently) and divide by number of houses. Fail. My own personal guesstimate is about 5% of homes. I wouldn't be surprised if it were more like 3%.