Lighting structure is separate from it's 'costume'. The lightning is then compatible with any/all festivities and we can encourage the community to decorate/make costumes for them.
The lighting system itself could be made 'intelligent'. They could sparkle as people pass by. Or if it were for halloween, they could play a 'spooky noise' as people pass by. They could be networked together, to put on simple, but coordinated light shows. The color and intensity of the light could play a role too. Think the blue gas light in Milwaukee... Blue on colder nights, Orange when it's warmer.
Ok, here is a thought that's getting out of control... Allow people to interact with the lights via the web (their phones). Each light could have a little 'dance' pattern... Or again, if it's halloween you could allow people to control what it says... as their friends walk by, they could scare them, or play something funny. Oh(!) Valentines day could get really cute with this idea.
Not thinking about the "costume" yet, the lighting