I am confused. If you don't print out your ticket after booking it (instead, you wait to print it until you are about to get on the train), you can cancel anytime before the train leaves and get a full refund. I do this all the time. I didn't even know there were non-refundable advanced-fare tickets. (I usually travel on the Acela, not Regionals, but sometimes I do take the Regional.)

The other point I would make is that a Regional train is unlikely to sell out before the 14-day window, so you may as well just wait until you're under 14 days out to buy the ticket. Since you are more concerned with flexibility than price anyway, why not do that?