Each PVE comes with one node that lasts the entire PVE, the one that has three loaner characters. That node should have a lot of prizes in it. Right now, it has 7 prizes. My idea is that it should have 4 + (3 x D) prizes, where D is the amount of days the PVE lasts. So a 4-day PVE would have 17 prizes, and a 7-day PVE would have 25 prizes.
This could be a chance to add in some unusual prizes, such as other boosts besides the Crit Boost (ie color boosts). Maybe even some CP, HP or Heroic or Event Tokens.