Also, Earth/Terra's Staff (for landing elegy)
Chanter's Staff (for buffs)
Demon Helm +1 (also buffs)
Cheap, low level CHR pieces like Noble's Ribbon, Bird Whistle/Flower Necklace, and many pieces of the level 30ish RSE (at least for Mithra)
Trumpet Rings/whatever the HQ is called
Since you've included ballad, the essential songs (for exp parties) are minuet, madrigal, and march for the front line, prelude for RNG and COR, and MND/INT etudes are nice to give the mages at low levels, before double ballad becomes available. Elegy, lullaby, finale, and requiem are all needed as well.
Of course you should get all of them. They all have some situational use outside of exp parties. Most of the "extra" songs are dirt cheap or sold by npcs, so it's not that big of an inconvenience.
~SMN99 BRD99 BLM99 BLU99 WHM99 DNC99 THF99 RDM95 COR95 SCH95 RNG75