In my experience I can say this, I donate as I know this is what pays the developers for their time in designing and upkeeping the game, You don't work for free so why expect others to? Also, I turned level 68 yesterday, and today I just got my last HopeBringers Relic plan. Donating has no effect on game play, except in what you do with the gems you aquire and the stated advantages to donating. As someone who has designed and operated donation only web games it makes no sense to give donators "Hidden" advantages. Tell them everything they are getting to maximize donations. So hidden advantages are imaginary only.