I don't see why we should raise aggressiveness. I've won several wars against England and lost several both before and after my victories. Increasing the aggressiveness would just ruin the game in my opinion.
I don't know how some of you go for 100s of years without being attacked. Try being excommed, try having a succession crisis, try having multiple people attack you and at the same time having revolts.
Try losing a excom war, having your treasury go away with the old king and having England, the HRE, and France figure now is a good time to attack you all the while your vassals in Brittany Normandy and various English ones as well start rebelling against the new liege.
Granted I've reigned in all my lost provinces from rebellions and was able to fight off the advance of these other countries with the help of other players in the game. But without them I would have lost a significant amount of land. The AI is certainly aggressive enough.
Who knows though, perhaps I'm in the minority.