The quests system is fine and all, but I think you have to be allied to or friendly with other factions to get quests.
I was thinking that, in much the same way as you can get map information from prisoners in Dungeon Keeper 2, you could learn about item stashes and raidable outposts by talking to prisoners.
yeah i always found it weird why other factions would tell me of resource stashes. at least some wanted some cash from me for the info, but still. you'd think if they knew about it they'd go get it themselves.
resource stashes should be found out from prisoners that you caught in a recent raid (imprisoning your own people shouldnt work in this regard)
outposts should still be communicated by other factions because everyone has trouble with pirates ;)