Okay, coming back to this a day-ish later and reading other people's opinions, I still am sticking with my vote of twice a year, and that if it changes to once that you still do something special in November.

However, I think I'm going to ammend my opinion and say that yeah, the idea of the fourth wall being part of a bigger plot, or changing it so that the characters do remember what happens (or both, especially both) would be a breath of fresh air and quite welcome.