First, get the musicians to learn to dance!
Get them, to understand that playing for a dance is not just keeping a steady rhythm - one experiment I've used in workshops before(but you need dancers as well as learning musicians)is to use one tune for three of four different dances - and get them to play FOR THE DANCE i.e. for the figures: - if they don't get the differences, they shouldn't be pretending to play for dancing - they're just beoing musicians that some people dance to.
If you're going to change tune during a dance, make sure that the change 'lifts' the dance and the dancers - this can be done through tempo, key, or just tune.