Intriguing ideas, and certainly the geographic and linguistic arguments lend weight. Especially in the light of a documentary I recently watched, which looked at James Mellaart, and his discovery of a Neolithic city in Anatolia, showing that urban civilisations pre-existed those of the Fertile Crescent. Not directly germane to the topic, but showing that looking in the wrong places, or not looking at all, can lead to errors.
I can also see how a history of division and migrations among a Semitic people would create an urge for reunification, both political and religious.
But as to what exactly Paul did and why, I'm afraid I must follow my ingrained cynicism. A mystery/fertilty cult such as that of Al-Issa would be palatable to Greek audience, thus making it easier for Paul to sell his product to them. For every true-believing prophet there are fifty con-men, after all. Just as for every four people with a real vocation, there are six who chose to be priests because they have a modicum of brains, the gift of the gab and a bone-deep aversion to actually working for a living!