Pat your point that going across the US to say Hawaii or even just coast to coast you get better aircraft typically than going to the Caribbean is what I have experienced. It seems they use the aircraft that are already used up a bit to go to the islands for the most part although we have had some nice ones at times but not normally.

Worst jets I have been on: #1 - Air India from Mumbai to Goa, it was hilariously bad, think of a velvet lined bus in India and you are getting close. #2 - British Airways 767 from Rome to London, while it was broken down on the tarmac for three hours I was able to trace the aircraft back to one of the oldest 767's in the sky although the staff was pretty good, aircraft no. #3 - AA from CLT to Nassau, I joked that it was a Dwight Eisenhower Signature Edition jet, but probably not as old as the BA 767.

Many fly a lot more than I, but I am presently flying a bit over 100k per year in the US, Mexico and Caribbean. It almost becomes sport between airline status and hotel status, will ride the wave while it works for me but someday that will end. Most is work related but I do like to vacation and I think I am pretty good at it!