I did something similar with my Dancer/Bard. Auto AoE of 4v6 centered on the caster, and I changed the abilities to standard charge times rather than continuous performances (just so I could balance things better). I tried to keep the class roles roughly the same (offensive dances, supportive songs), but I also tried to diversify the skillsets a bit. Mostly I wanted to replace the stat buffs and debuffs, to keep Squire's Accumulate and the Knight's break skills unique.
I like your idea Vanya, of having Dances keep infinite range but with line of sight restriction. I just did mine this way to keep the two classes as closely parallel as possibly.
Gratuitous promotion of my own skillsets:
Dancer - rather than acting like the dances themselves have an inherent power to their steps, I'm attributing the effects of dances to the discreet use of various poisons, smokes, and mild enchantments, representing the Dancer as a manipulator instead of someone who can turn people into frogs just because of the way she moves her body.
I won't explain how massively I overhauled my job tree, but the two main requirements for Dancer in my patch are Thief and Wizard, and that's the sort of flavor I'm going for.
Venom Dervish - 10% max hp damage with a chance to poison
Sapping Aura - 25% max mp damage
Dusk Minuet - ~90% chance to add darkness
Hushing Pall - ~65% chance to add silence
Lethargy Mist - ~50% chance to add slow
Nameless Dance - ~70% chance to add random status
Water Rondo - ((PA+4)/2)*MA water damage (inspiration from Mog's FFVI dances)
Bard - Bards are powerful because their songs/stories inspire. And, there's maybe a little bit of magic behind them. Their two main job requirements are Priest and Warrior (overhauled Monk), so I'm treating Bard more like the badass Norse Viking Bards rather than dudes playing lyres in tights. Not like there is anything AT ALL wrong with that.

Also I sort of built these guys to be alternatives to using Priests and Chemists as your main healers.
War Epic - heal 10% max hp with 100% chance to add defend
Mystic Melody - heal MA*2 MP
Soothing Song - heal 10% max hp and dispels negative status ailments
Uplifting Hymn - ~65% chance to add faith
Vital Anthem - heal 20% max hp with 25% chance to add regen
Myth of Gods - (MA/2)*MA holy damage, with chance to add regen (felt they could use an offensive ability, but only with a drawback)
Unending Tale - ~80% chance to revive teammates with 10% max hp
Oh, and I got A LOT of inspiration from Final Fantasy V:
http://finalfantasy.wikia.com/wiki/Dancer_%28Final_Fantasy_V%29http://finalfantasy.wikia.com/wiki/Bard_%28Final_Fantasy_V%29I included the abilities I used above merely to illustrate the point that Dancer and Bard can still fill the same sort of roles they did in Vanilla, but with maybe less of the silly brokenness of bland, map-wide stat point changes. Regardless, I like where this thread is headed.