boosting other factions typically widens the differences between factions and helps them seem more unique. on the downside it means that their is a steeper learning curve. personally i wouldn't mind a steeper learning curve.
having all of the extra pop go to your capitol, means that when it gets full you stop getting any advantage from being aggressive. having extra pop (growth beyond what the city has room for) go to the rest of your cities would open up more options for playing them. having the undead settlers cost the same pop as they provide in a new city (3) might help with early expansion (at least for land grabbing), it would also make it easier to use consulates to boost the g