Here's how you do a Halloween event in swtor: Have the players visit the wreckage of Malachor V, where you have to fight waves and waves of mandalorians, and finally end the planet with a Darth Nihilus boss battle. True Star Wars fans know however, that when Meetra Surik left Malachor, it crumbled, so make the entire planet a nightmare WOOOOO!
You could also have a trick or treat event on the fleet, where you can buy a mask that looks like a space skeleton or space pumpkin or space mummy. You go around to different npcs, and they'd give you random loot and maybe a candy buff for 60 seconds, which maybe changes your appearance. The candy buff on the imperial fleet could have a chance to give you the razor blade debuff, which just makes you move slow or something.
Those were all pretty crap ideas, but I think it's important for an mmo to have holiday events. It builds a bigger sense of community, and makes the world feel alive. If we don't get our real world holidays in game, then I would really like to see BW add a couple fictional holidays to the SW universe.