@aldrien:
For me, the best DM spice was always the ones that managed to pull whatever your group was doing into whatever the big server wide plot was at the time. You're doing Ashby Sewers and as your'e going along you run into odd creatures that are giving instructions to the orcs and at the end, there is a "evil plot NPC" making a deal with the Ashbys that teleports away when you are close to capturing him in the final fight.
This, IMHO, was the best way to involve people in what was going on with the server. It only makes sense that if I'm trying to take over Arabel, I get some inside help, so yes, outside evil bad guys will try to co-opt inside evil bad guys.
I always thought the Ashby's end was rather ignoble and left a vacuum that has gone entirely unfulfilled. They were an established presence in the region, with a full scale storyline and reason for their recurring maleovolence, while not becoming a true full on city threat like an army, or some epic super-magic apocalypse.