If you're interested, I have lots of notes about spirit possession - that being a 'sickness' that comes upon a person when they are possessed by a spirit. Rather than exorcising them, the thing to do is to accommodate the spirit, which normally only wants you to observe a few taboos, in return for which it grants special abilities. This kind of thing is VERY common in the middle east. In fact, there are proper 'muslim' spirits, which require the person to observe the various Muslim cultural avoidances. In Africa, they are called majini or mashetani, depending on their nature.
Also, Muslims and other Peoples of the Book like to do book sorcery, using phrases from their holy books to procure certain affects. These phrases can also be made into amulets or medicines.
Here's the
thread where I tried to work Similarity and Contagion into RPM.
I rather like your ideas, BTW. In my Refugium setting, I'd planned on having a continent called where the Zoroastrian religion survived and flourished. Bundahisn is the Land of Prophets and is regularly swept by waves of fairly peaceful religious fevor. The underlying culture is Persian mysticism, but there are sects that resemble Yazidis, Zurvanism, Madaeism, Manichaeism and Mazkadism.