How about adding the ability to speed up the rates of production for Farms and Mines.
In Clash of Clans one of the best uses of gems was to double the rate of production for a mine or elixir collector for 24 hours. It was usually a small amount needed to do the boost.
It was still using gems, but was much cheaper than the option to instantly fill your reserves.
I know many people hate excuses to spend gems, but I think many would use this.