Current updates have recently improved your ability to receive gems from obstacles; however, it is not a guarantee. The gem boxes, the only obstacle that has a garuntee on gems and was added in the last update, was the only sure way of getting gems besides achievements. The higher up in the clash rankings you go, the harder it is to get gems besides paying for it. The easiest way to balance this out is by supplying players 10 gems for every 5 levels you go.
