Not sure if anyone else agrees with this idea but after you have either purchased, with real money for gems so that in turn you can purchase a Gem Pit it does seem to go to waste once its depleted, yes ok you may well have brought thousands of cookies, golden parrots or silos but what if when the Gem Pit depletes you get a mystery gift, maybe an adventure, X3 or X4 buff or something along them lines so that you will be A) promoting the reason for buying gems (to get a Gem Pit) and B) making the blow of losing a gem income that little bit more easier.
Let me know what you all think
Cheers
Hammersmith