I started dancing ballroom/latin when I was 16 with my then girlfriend, danced for 6 years in a row and then quit because I moved. While I was still together with my then girlfriend at the end of it, I've had ample opportunities to hit up girls in the class. I've had at least 4 girls fall in love with me during dancing(even tho they knew I had a girlfriend).
Later I started dancing salsa and I recently returned to dancing ballroom/latin again. Trust me, all the girls think I'm so awfully gay that they do nothing but flirt me. I've made out with 2 girls from my dance classes in the first 3 months of the classes and recently I've been having quite some good rapport with 2 others. During the salsa classes I banged 1 chick but that's because the group mainly consisted of girls over 30.
Dance classes *ARE* a good way to learn new girls, but as said by others, do it to learn to dance. You can use your moves on the dance floor in a club, or just show girls how to dance a bit. It's great kino, easy to escalate and collecting numbers *IS* easy as hell. I got some pretty slick dancing moves I can use on the dance floor, and even if none of the girls are interesting, you can hook up with them, take em to a club and do a bit of dirty dancing with em. Social proof that will pull outsider girls into your group pretty quickly, and with a wing you can isolate them.