Or does it not affect other dances besides waltzes?
Steps are fixed percentage of stat down. I guess CHR could alter duration, but since landing them is based on accuracy, you'd likely want to be using them in TP gear.
Flourishes are either fixed effects or depend on accuracy, so same as Steps.
Sambas are fixed duration, with the drain/aspir effect based on weapon delay and damage dealt, and the haste effect being constant (afaik).
Spectral Jig is a random duration (don't know about Chocobo, still 3 levels away). I guess CHR might help duration, but you'd never really be able to know for sure.