I own two vintage cars, a 65 Fairlane and a 62 Thunderbird.
The problem with 'smog' laws is that these older cars really cannot be brought up to specs short of a total redesign. Many of the great engines of the 60's and early 70's-the 351 Cleveland, the 427 Side Oiler, the 327, the 427 Rat, etc. were killed off was because they couldn't fit into the smog testing. Retrofitting some of these cars might bring them up to some kind of smog standards but the cost would be prohibitive and destroy the 'original' value of some of these cars.
I do actually drive the 65 Fairlane on a regular basis. I restored her to drive everyday to work. Her mileage isn't any worse than a Grand Marquis or any other car of her size. I think old cars should be inspected for mechanical defects, mostly for safety reasons, but smog proofing them is pretty stupid if you ask me. I would also say it is illegal, it is an ex-post-facto law and something that probably wouldn't make it through the courts.