Even though I agree that Halloween doesn't fit with the SW universe, the real reason you have these kinds of events in games like WoW, GW2 and Rift is because it gives players a nice distraction from the same old same. WoW has so many holidays now that there's constantly a new one on the horizon.
I think it's safe to say that we need more content for time sinks when that 5th alt or 400th warzone gets old. Whether or not the BW team currently has the budget to grind out that kind of content is really questionable.