It's actually not that bad anymore. I noticed the invites really flare up to obscene levels in Valkrum Dunes and the Maze of Shakrami (and the adjacent areas). It must be a level range issue. People in areas weaker than those don't need parties, and people in areas higher than those already have established groups. Since I'm level 16, and in the process of preparing to get a subjob in the near future, I've been spending quite a bit of time in those areas (darn Ghouls).