The Bard Elemental/Purifying A Cappella songs seem to be worthless as they don't put you over resist cap and by the time you're able to get them everybody is already well over. Maybe they can use an upgraded Mana Regen, AoE damage, damage shield, attack slow, DoT, or even just an over-cap resist buff in place of those
There's a rune in that song which is nice, though I was not aware it blocked all damage from 1 source as bubbin is stating.
My shamans resist spells are worthless though, they dont add anything but the resist, which are capped pretty early with gear