I've always felt the vault frustrations are more symptomatic of another problem with this game, not a problem itself. The way loot is designed now, it's pretty difficult to get attached to a few core pieces. Everything is random, from the gear we get to the qualities it has. I think a loot system that lets players go get the gear the want, modify its appearance to fit their tastes, and tweak its performance to suit their playstyles, would really eliminate the need for large vaults.