I have came up with a little idea of adding in not a few goblins here and there, but packing yourself up and bringing the elite from different guilds invade an enemy city!!! Waw i think it would be the most intense and fun Oblivion play possible. With the mages and fighters for cover climb the walls and ransack the place. You could act as General ( i have such a mod ) and command your army to victory

Initially poor levies get slaughtered by your people on the walls then you can pillage their shops and houses killing everything. Then on to the Keep where the Elite and their bodyguards fight to the bitter end to defend their king, Needless to say they die and you win.
As for NPC's to use, using Oblivion NPC's to make an attack and die then respawn wont work. Instead a large group of Morrowinds finest travel over from Morrowind to aid you. A chance to fight alongside your old guild buddies.
After the town is taken you could make yourself the towns new leader and with the houses available your guild buddies can take up home there. Maybe encouraging other people from other towns to come and work for you. We dont want to be the best and live like a common, we want to be the big guns:D
As for this to work i would like some modders to take this up, even just the ransack of the town. However i have made a mod for Never Winter Nights similar to this in terms of the battle but i have no TES experience.
I would appreciate direct feedback by email please @ vicious111@hotmail.com