If you have an NIE, does that avoid having to pay the 12% impuesta on cars?

If you mean taxes on importing cars to Spain - I don’t think so no, maybe have a look here

http://ukinspain.fco.gov.uk/en/help-for-british-nationals/living-in-spain/cars

to be honest I am not sure having an NIE saves on any taxes ?? That is more to do with being fiscally resident.

I don’t think having a NIE will avoid paying the tax like the others said. We just imported our car from Italy to Spain and had to pay all the taxes. I know in the canaries, you dont have to pay one of the taxes if you have been the owner of the car for at least 6 months before bringing it to spain, but then you are not able to sell it for at least a year. In addition, you will also have to get the NIF to get the car transfered over (a painless process). In the end it cost us around 2000? to transfer our car which is book valued at 5500? as in addition to the 12% we had another tax we had to pay that was around 10% plus the city tax and another 90? to trafico.