This much I know:
Must have a mirror ball
Encourage 70's/disco dress

And here's a bunch of questions/ideas:
Need a DJ - all seventies music? videos too?
Need an MC for the evening
Get Katie Pittenger or someone to do a few Donna Summer, Gloria Gaynor songs?
Karyoke?
Have a dance off? (Lena Kennedy's idea! I can't take credit.)
- Dance off could be set up like Soul Train Line
Teach dances like the hustle and the bus stop?
Fashion contest? For adults and kids?
Should we have activities for kids elsewhere in the barn?
Should we have "baby sitters" elsewhere in the barn?
Food? Should we charge?
Drinks? Should we charge?
Served in seventies lookin' containers?
Prizes?
Goody bags/gifts?
Decorations?
Name tags?
What can we do to encourage or highlight connections?
What can we do to encourage all kinds of diversity in attendees? Dare we dream to get teens there?
Where should we advertise?
Activity idea - what's your seventies name, like what's your Bad Girl name - www.badgirlswirl.com (click on Alias Finder)
How can we use social technology to support, encourage, enhance?
Security?
In advertising create an Instructable telling folks how to get ready for the dance - www.instructables.com - things like - 1. Go to Value Village. 2. Seek the following types of clothes - bell bottoms, satin jackets, tube tops, bannana colars... 3. Use the following resources when applying your make up for the evening (find an online resource for 70's make up.) 3. Pracitce the Hustle (find an online resource.)

Also need to determine:
Budget?
Charge to enter?