Originally Posted by
CPH-Flyer
If booked with ANA miles, you can potentially buy a premium economy seat at the airport.
You can upgrade to J with miles on a cash ticket, if you have the right (read rather expensive) booking classes. When you select flights on the ANA website, it is quite clear whether the selected fare allows for upgrades.
I don't think so. But even if this is true, pay cash to upgrade at the airport is never a good deal in general.