Gameplay change - remove piety cost for unanswered prayers
There are many things you can pray for in ADOM - but as every attempt to do so reduces piety, players are loath to do it, so they experiment with them extremely rarely.
This is a substantional negative gameplay element, as players miss on all the interesting minor effects that they could've discovered otherwise.
I don't see any real reason for an unanswered prayer to reduce piety - so I suggest removing that cost altogether, and if you have a holy symbol equipped - to even generate a minor boost instead.