Small update... I just spent the week in Denver, where they card everyone - and decided as an experiment, to only carry my PR ID.
Aside from the novelty of it, there were no problems with it. One person at a recreational dispensary asked for my passport - a quick "PR is part of the US" resolved that (oh yeah! I forgot!); and one bouncer at a club had to ask his manager "do we take PR ID's?", but that was resolved in seconds.
But that was in a fairly progressive well-educated city. I'll try that out in a place that's not so exemplary and follow up.
As far as the airports involved - SJU, MCO, DEN, and MIA - the ID was a non-issue. No questions, no raised eyebrows, no comments.