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 growth of a town.
having the viable town locations not take into account the presence of food can allow you to colonize a wasteland. while the enemy can still sack your cities, he can't use them against you (and hopefully has to use resources to take them). that should help save mana on terraforming spells as well.
having them retain their undead specific assets (such as not using food, or wageless units) when using them for a custom faction would allow you to make a kingdom custom undead (for the life spell that boosts growth). didn't notice new scroll bar in unit traits window, maybe 2 points is a bit high for the ability though.
if these things were implemented it would make them easier to play, and the under the hood stuff to make these work would make it easier to implement other unique DLC factions.
edit: well i missed the scroll bar, so the only suggestions left are ones that help the AI as much or more than the player.