It may depend on how much you were hoping to accomplish (mileage-wise).
Between exploring the wilderness trails, swimming in Lake Michigan, and playing on the dunes it seems like there should be plenty to keep 14-20 year olds busy for a weekend. Depending on logistics, it might be more base camping/day hiking than backpacking since you're going to want to be near the beach for a beach party.
In addition to the wilderness area trails, I've hiked South along the beach to the lighthouse at Ludington State park and back. Maybe 10 miles round trip? One possibility would be to stay at the state park one day, backpack up to Nordhouse for a day and camp there, then hike back out to the state park the next day.
This site says that there are about 20 miles of trails in Nordhouse. I wouldn't have guessed there were that many but never really tried to add them up.
Here's the map if you or anyone looking hasn't seen it before:
edit: Just so you know, I encountered the worst Mosquitoes of my life at Nordhouse and Sleeping Bear in early/mid June 2007. It was worthwhile to stay near the water/breeze to keep them at bay.