I was discussing changes they should make to guilds with a few party members the other day. Here is what we came up with:
1. Guild bank added to the character bank locations that allow not only for item storage (like the ship chest that get ninja looted) but one that other members can add money to for ship amenity cost.
2. An experience and renown bonus for guild parties and raids.
3. New amenities. There are plenty of guild levels (say 64-69) where there is room for +3 stat shrines and maybe 40% resistance buffs.