I'm voting for two a year, because of the many reasons other people have given (it's fun, chances to play with characters you might not otherwise, ability to play with character powers in the setting). But also because one of the things that's useful and sticks around ICly from these events is the opportunity to put your character(s) anywhere on the map once they're over. With Route being spread out over such a big area, I think it's really useful to have that option for characters who don't travel much ICly but the mun might want them to get out to new places, or to get in-person CR for characters that never seem to be in the same place.

I definitely agree that if we keep having them twice a year that they shouldn't be the only event of the month, and so much agreement for having some kind of bigger plot with them or keeping the memories. I think that would make it seem like much less of a 'wasted weekend'. Adding anything new or different would be great, since as one of the people who's been around for all of them it's difficult to keep coming up with new and interesting ideas.