Same issue, pretty sure it's a bug? All I did was rescue 3 hostages from the Missing Caravan mission and I got a gold coin + went from lv.15 to lv.37. It was nowhere near as rewarding a few versions ago.
happened on ver 9.8.0.6
Yes, didn´t mentioned the tons of Exp. you also get. The Wiki says it should be 5000 per hostage.
------
It has to be a bug or otherwise wrong implemented thing, because it´s totaly breaks the economy and but not least the "longtime goal" of reaching 20-30 Goldcoins to leave this place.
I mean i play this game for just a week, but i am pretty sure this isn´t intended, compared to how other stuff is rewarded.