Well, it depends by one's style of gaming. Even if EB is really great, I personally find a little boring to play when enemies are silent, nothing happens and I only have to cyclically press the end turn button and wait for something, then repeat. Expanding the settlement-managing part would give more complexity to the setting and require more involvement by the player into the mechanics of the game, enhancing his gaming experience. Besides, it could also avoid rushing empires that in less than 100 years have become strong, heavily developed and large... strategic game will be more long-living, hard and interesting.

Another possible add would be the fact that players should also consider that fields get poorer if exploited, so every year they will have to rotate them (i.e. one year grain-livestock-resting free field, second year resting-grain-livestock, third year livestock-resting-grain and so on) otherwise fertilty will decrease - however perhaps this is impossible with the engine of Rome, and I think that it would also be terribly boring and repetitive to do every year with a lot of settlement and farms to manage. I remember an old TBS/RTT of about 12 years ago, Lords of the Realm II, where this was possible because maps were small and provinces low, so one hadn't troubles in managing every settlement... but in a huger scale the matter is completely different.