I have to admit that I did not read through all four pages of posts, but in response to the creator's "under considerations" in his/her original post, why not have the Islamic Missionary be a Sufi? Sufis, if I am remembering right, were missionaries who trained in monastery like buildings. They were responsible for the spread of Islam to Indonesia (in addition to merchants), and I believe parts of Central Asia and western Africa. Don't quote me on the western Africa though. They were compared, I believe, to the the Jesuit missionaries/monestaries of the Christian Catholic Counter-Reformation (I can't remember whether the Sufis were Shi'ites or Sunnis though). Hopefully I haven't mixed up too many facts- if I did and inadvertantly offended you, I'm most sincerely apologetic!
Here's a link to the wikipedia entry on Sufis. There's alot of material, but pertinent information in regards to the role of Sufis as missionaries is in the paragraph I've copied over below (I'm sure there's more in the article, but it's a touch on the lengthy side).
http://en.wikipedia.org/wiki/Sufism
After having gained influence over the whole of the central Islamic world, the brotherhoods (turuq) became the focus for Islam in the new territories that came under Muslim domination or influence. This included the Indo-Malay territories in the East, and West Africa and Andalusia in the West. The brotherhoods made a significant contribution throughout the centuries in presenting the true face of Islam the Islam of beauty and love.
By the way, nice idea to include Zoroastrianism, and if I could figure out the technical part of downloading mods (I haven't been able to get any to work so far), I would certainly do so with this one!
One last suggestion, though, perhaps include a "Favored religion" for individual civilizations? You'd have to add another faith- perhaps broadly labled "Pantheism" or other appropriateness for the Aztecs and Incas, and perhaps the Greeks, Romans, and Egyptians as well, although they could be characterized by the Christian and Islamic faiths that the majority of their citizens follow today. This would of course mean that there would be no Jewish civilization, but I can't come up with all the ideas!