I see it like this. Why would any American or Canadian, with any scruples at all, attempt to import a car temporarily and then apply for UCD plates which allow you to avoid the law by paying a fee and it is backed by an organization that we know very little about? Doesn't make sense. You are limited to the area you drive in and I don't know if you can get regular insurance or buy it through the organization.
Any true-blooded American, Canadian, or Mexican would be more than happy to contribute to the coffers by paying for importation, plates and tags. I have seen Mercedes driven by Americans in SMA who have joined the association.
I understand, "when in Rome do as the Romans do", but I doubt it was ever meant to "screw unto others as they may or may not have screwed unto you".