I'd go if you still are friends with a lot of the girls...and if he's a sweetheart nominee, he probably knows a lot of people that will be there too, so it's not like a random date that won't know anyone, you'll still get to socialize with everyone!
BUT! This is what my chapter is doing about dresses (our formal is on April 16th). My roommate is a Chi O also, and we're throwing a dress swap party on the 9th! Everyone brings their old prom and formal dresses, and I'm making racks that they'll be able to hang them on when they get to our apartment. We're gonna have snacks and cocktails, and get to hang out with our sisters while finding a fabulous dress to borrow for the dance on the cruise! So far we've gotten really positive feedback, and a ton of girls say they're going to come, which is good, it means more options for everyone to find their dress! I know this is probably too late for some of you w/ April 3 formals, but maybe for next year it would work.