Shattered Kingdoms

Does art (spellpower) affect saving throws vs songs, or is it only charisma+lvl? There's nothing in the art helpfile about songs, just spells. Mechanically does dancing lower others' resistance or increase the power of a song? Same question for ensemble.

Art does matter for saving throws vs. songs. Songs do not get mentioned in the art help file, but art does get a mention in the chord help file. There is no single, straightforward answer about how dancing and ensembles work with regard to saves and art. It is different in the case of different songs. I also can't tell you for sure how ensembles interact with art. Generally, ensembles make songs harder to save against and dancing increases the range of effects of songs. Both can increase potency.