So I've been thinking of easy ways to make the AI more challenging without too much coding.
Why dont you do what Fawkner did in W2 and basically make the AI all "Declare war" after 10 turns or so and set them all up in an alliance to attack the human player. That way they dont attack each other and concentrate on the human. I know it seems kind of unfair but it did add some challenge to hotseat play.
Another idea is that you could add code to the AI to give them no hidden map when the map is still hidden for the player.
Just some thoughts.
Ken