As with Lullaby, Apollo's Staff is also the most effective boost to the newest White Mage spell, Repose (a light and divine magic based Sleep II). For less resists and partial-resists, there's no more bang for the slot than this staff.
Aerisss, you *NEVER* get +1mp/tic from any avatar without some sort of +refresh from gear, or Sanction Refresh. Only way to get +1/tic is with apollo, carby mitts, and vermillion cloak (Unless you decide to get Sanction Refresh, then you can get it below ~80%[?] MP with austere robe)
Hidden Effect
+15% increase to Light Element Magic Spells
-15% decrease to Dark Element Magic Spells
Charm success rate +15%
-3 Avatar Perpetuation Cost for Carbuncle and Light Spirit
+3 Avatar Perpetuation Cost for Diabolos, Fenrir, and Dark Spirit
Sakka has been rated down even though his comment is right. An avatar will ALWAYS cost 1mp/tick regardless of how much -perp you have, this is removed by the summoners trait, auto refresh.
you can have smn af2 body, head, af+1 boots, mitts, HQ staff, on lightsday with light weather, and you'll not get +1 mp back without sanction on. however swapping in an auto-refresh piece will.
If they were to make the Cure Potency on Apollo's higher than Light Staff, they would have to change all the other HQ staves too. i.e. Vulcan's Would be Attack and Ranged Attack+15 (originally 10) and Terra's Staff would be -25% Damage Taken. I think the hidden effects alone on these staves makes them worth the gil.