I like those ideas as being challenging events for level 40 or 50+ characters. Could add a lot of tension and fun later when things start getting a bit repetitious.
I had a town invasion idea too, recently. It involves a boss monster raising an army at one of the lower dungeon levels, and then marching on the town. They'd travel on foot, sticking together around the boss on their way to the stairway leading up on their level until they finally emerge from the dungeon entrance to attack the town. Then of course, there would be a quest to stop them before they make it to the surface.
Not sure how much of a pathfinding horror story making that happen might be though.