Any opinions on the stretch seating? Is it just seat pitch, or are the seats a bit wider too?
It is just seat pitch. The seats are not wider. In regular economy, I can't work on a laptop if the passenger in front of me reclines their seat. However, in Stretch, it isn't a problem.
BlueHorseShoe2000 makes several compelling arguments on keeping your 1K status too. I would say that 1, 2, and 4 apply equally as well at Frontier too. IMO, the lack of a global alliance FF partnership is Frontier's greatest gap at this point.