Since it's tailored to reach the right people, in this case by looking at previous participants, it seems reasonable to me to try.

I love the ideas about a QR code and about making it a postcard.

To throw out another idea, have you looked into business card ads? I've noticed that some bars I dance at will have a table with 2-3 little cards tossed on there that advertise other dances. I like it, and I think others do, too. If you like one kind of dance, there's a good chance you'll like another, so it doesn't feel like litter or like attention grabbing. It feels like dancers sharing clues with each other.  -Lex