According to the Korg Rep, the reason the polyphony was increased was because the Guitar mode gobbles it up.
If you compare the PA1x and 2x side by side, you will find the sounds to be quite a bit better on the 2x, (At least when you compare them to Real instruments, rather then other boards) however whether there is a big enough jump in quality to upgrade, each owner will have to decide.
BTW there will probably be some good deals on the remaining PA1x, so don’t dismiss it just because the PA2x has come out. (Remember a great player will still sound great on an older keyboard, and a bad player will still sound bad on the latest keyboard)

Bill