I'm doing a steampunk costume this year too. No, it's not anime related excatly, but it is science fiction/fantasy, and that's close enough for me. : ) Besides, one of my favorite steampunk novels has just been released as a manga, so there ya go... it fits in perfectly now. ; )
I agree with everyone else though. The con isn't about cosplaying, that's just an added bonus. I like to be able to wear my steampunk outfit as often as I can, and NDK is just another excuse to keep changing the costume, and come up with new weapons and other fun stuff.