Maybe it's time to think about some new bonuses, like a guild bonus for Vitality Regen and for Stamina Regen.

Many guilds have maxed out the current bonuses, and Citadel level 10 is crazy with 2.5 million militia needed. Not many will be getting that one anytime soon. There's no reason that you can't offer more levels to the current bonuses and add some new ones.

Some possible new boosts:
Vitality Regen
Stamina Regen
EB attack %
IPH increase
Alliance Attack and Defense
Plus Health
Energy back

Extend the existing boosts especially:
More Health and Energy Regen