living in California for 20 years drives the 'dirty car bad' meme into you quite firmly - I wish WOFs tested emissions the amount of crap spewing on NZ streets is really sad
I really think a policy such as this implemented in NZ would further see the flow of money from poor to rich. In general poor people own older and less 'clean' cars, emissions testing for the public would only penalise people with no money already, while richer people with newer cleaner cars will most likely not have to pay anything to pass an emissions test.
I would prefer it if the onus was put on to car manufacturers to meet certain emissions standards which are raised every 3-5 years or so, increasing the amount of clean cars from the top. It would take longer to get emissions under control, but at least it would protect those on the margins who need a car for work, but can barely keep it running as it is.
I'm not quite sure how you would tackle the problem of imports though.. Maybe anyone importing a car has to pass an emissions test, although maybe not as strict as the one for new cars.. *shrug* I dunno.