How about you do a famine war every 4th war?
No power up/boosts or alliance wealth advantage.
Still have the rewards for afterwards.
Basically it becomes man on man with the exception of alliance size but it fosters a higher level of participation as mid to small alliances can compete by higher participation and not be locked out due to every power up enabled situations. I understand there is a financial issue but there is also the joy of a level playing field in gaming, offering this occasionally would be a nice treat for most of your users. ( and welcomed by 95% of alliances)