Those laws are stupid. A person ought to be free to import any car they want from anywhere in the world regardless of what it is or when it was made.
I'm OK with the car having to pass USA emissions. Stick a sensor up the tailpipe and confirm it's compliant with the laws in effect for its model year. That affects everyone else. Make the buyer pay for that test. Totally reasonable.
Your point about headlights, etc. is also appropriate. Things which could affect other people should be compliant to the model year. Again, require the buyer to pay for an inspection which generates paperwork acceptable to the DMV in your state.
But they ALSO demand that it conform to NHTSA
passenger safety standards at the federal level. That affects ONLY the buyer and any subsequent purchasers. So, have a disclaimer form which the buyer must submit wherein they acknowledge the unknown interior safety situation and accept liability associated with it. No one external to the car is affected.
I can speak from personal experience on this one. I wanted to buy a 2009 British car in Canada and bring it back to the States. The manufacturer didn't want to have separate versions for the two markets so they exported the same car to both USA and Canada. The cars were so identical that this Canadian car had a United States EPA sticker on the engine certifying that it passed US EPA requirements! But Canada has its own version of the NHTSA, so it had a Canadian "safety" sticker instead of a USA one. Bang - case closed, the feds say you cannot bring it into the USA for ownership.
You may be able to get it here, and some states will even title and license it. Some people have done that and just take the risk. But if the feds find you driving it they will seize and crush it. That's the law. Never mind that the car is identical to US safety standards for 2009. Never mind that the only people affected by any potential substandard safety situation were the people INSIDE the car. Nope, your only real course of action is to wait for 25 years to elapse.
By the way, Canada's "25 year rule" is just 15 years. Still too long, but hey... lots of people point to Canada as an example of a better way to run a government, so how about we start with this?
Grrrr.