That is the first time I have heard of personal choice dining being overbooked, although I have heard of lots of people who tried to get traditional dining and couldn't. It seems clear that more and more people are becoming converted to PC. Princess may have to make a section of the traditional dining room available for people who want PC dining. We found on our cruise that there were a number of people who had booked early or late seating, but then decided they wanted the flexibility of being able to eat anytime and never went to their seating. I think that is really not right, especially as I heard on our cruise that they could not accomodate all the people who wanted traditional seating times. There were apparently empty tables in the trad. dining room night after night.
We never did get to the alternative restaurants, but they seem to be a good option. It cost $8 pp for the Mexcian one, but you get a large Margarita with your meal, so that is a good deal. Sabatinis is $15 pp, and you don't get a drink with dinner, but brunch is really a bargain - you get unlimited drinks, either Mimosas (Champagne and Orange juice), or bloody mary's or a couple of other drinks.