I suggest that there is always a doctor npc, as dealing with curses/diseases after you've used up the buildings that give blessings can be rough. There should be only 1 doctor per map, and maybe the cost would be random (not too high/low, or maybe scaling the cost like with the donations to gods.).
If you think about it, about getting happyness, the cat that wants you to pet it's belly gives 1 happyness for 0 gold, does that mean the cat is better than the Jester, and blacksmith, and the others...
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