Muslims being crushed by catholic great powers

[Trin Tragula]

You can't realistically argue that the MP in NA should be increased.

Why not? Historically Portugal seems to have had a smaller population than Morroco in 1500 (Portugal: 1.1 million and Morroco 1.5 million). In the game mainland Portugal has a base manpower of 23 and Morroco one of 15.
From experimenting some with all of this my view is that the AI will always strike at regions it considers weak. When I've tried increasing the base values of North Africa and Turkey the result is that Spain, England and Portugal starts doing naval invasions of Scandinavia instead.
For some reason they won't go for medium wealth or rich regions but will prefer regions with really low tax and manpower values. This imho is the root of the north african annexation problem in EU3.

EDIT: I should add that my source for historical population numbers is Angus Maddisons "Historical Statistics of the World". I believe it is available here: http://www.ggdc.net/maddison/content.shtml

 

[Trin Tragula]

Making certain religions more susceptible to conversions is very easily done though. Conversions are much too easy in general in this game. It often creates vastly ahistorical situations not only in northern Africa but on that entire continent, as well as in India, China, Indonesia, etc.
This is a very general point though. I still think the specific problem with North Africa has more to do with AI priorities than anything else. I do feel tax and manpower are too low and the provinces are, even if better than in some parts of the world, sometimes a bit weird, but that aside the problem is really that Castille is interested in the area at all. In my experience they will attack even without their mission to do so and they will certainly do so without the holy war CB (but not having the CB means they will expand a bit more slowly).
The problem as I see it is that the AI will always go for enemies that are much weaker than itself even if it has very little to gain from doing so. As I said before, just increasing north african province values some will make Spain and Portugal ignore the area but they will just turn to Scandinavia instead. Spain and Portugal have very little to gain from either region but will attack just because they can.
I'd be much happier if a strong AI power like Spain attempted to dominate Italy than just conquer a bunch of tax 2 provinces and to then sit on them.