I did a little more testing last night, and one can get some quite interesting results from playing around with the provincial bonuses.

I'm not totally certain, but it appears that if you put a bonus for more than one unit type to a province the AI will attempt to build the buildings necessary for both I tried this in Scotland, where i gave a provincial bonus for the celtic warriors in addition to the highland clansmen. Lo and behold after building the castle the AI did eventually build the necessary swordsmith for the celtic warriors.

One thing i didn't try, but would love to see the results of, is to combine a province bonus for a land unit and ship unit in the same province? Due to the shipyard requiring a castle4 (in addition to port), the AI seems to have a problem with bonuses for ships in provinces which start completely undeveloped. In the native game that includes Tunisia if Muslim and Portugal if caravel-building Catholic. However, if these ship bonuses were coupled with a bonus for a land unit, then one might see the AI coping better?. Certainly one to try.

One interesting point is that if another faction takes over a province in which it cannot build the unit with the bonus, then the AI simply builds up the province normally.

It's still difficult to decide what is more advantageous for the AI in the long run, as everything isn't crystal clear. Norway has a +1 for vikings, but the AI Danes will build it up further as the game progresses. Cyrenacia has a bonus to Saharan cav and Morocco Berber camels and the Almos will stay very specialised in these provinces. By removing many of the Almos province bonuses i've got them to build gold mines in all 3 of the N Africa provinces.

By sticking a bonus for Swabian swordsmen in Swabia, i can get the HRE to start building them very quickly indeed By adding bonuses to provinces for units that require a lot of tech, one can focus the AI to build certian unit types much quicker than before. They'll also get the benefits of all the other units that are able to be built from the same buildings lower down in the tech tree. Chivalric knights automatically spring to mind as a good example for the Christians and Faris/Ghulam cav for the Muslims.

One thing is for sure and that is one can definitely get an improved AI build strategy with a few strategic alterations here and there. Egypt, Tunisia, Morocco, Portugal, Wessex, Mercia, Tuscany, Constantinople and Castile are obvious targets, where the bonus impart poor AI build strategies. By removing the ship bonus in Wessex thereby focusing Wessex away from immediately building ships, one can somewhat prolong the existence of the English as they'll initially build more troop producers.

Next to try:

Provinces with bonuses to ships and units, e.g. Venice with Italian infantry and Galleys.

Regards