Turning a clearly melee-focused unit into a caster is questionable. If you really want to speed up the Dancers, there's an ability called Charge.
Well, "caster" sounds strong, but he only has 1 attempt. =)
Charge lasts for 3 turns, and they already have high initiative.
Just to clarify, the Dancing with Death unit has 15 Initiative!
And Charge adds another 8 Initiative.
A general speed boost is already a bit much (I'm thinking of lowering it to an initial +10%), and Charge... that's not a Tir upgrade for the unit at all.