Whatever you do, make sure it's "cool" temperature-wise. The last event I went to was PACKED. Like to capacity full, and hot as HELL with MAs carrying around hors d'oeuvres and cocktails. It was INSANE!
Anyway, I wore a white collared shirt with a tight black pull-over sweater vest, dark washed jeans, and a pair of black t-strap heels. I was comfortable and not over-dressed or underdressed.