I can tell you for a fact that after a big hit like Hellfire or Memento, Curaga only ends up healing the two lowest members for like 1300ish each (so it's like two Curas for the appropriate mana cost, but casts faster than 2 Curas in a row). This makes me think there's a capped pool of around 2600ish (depending on your Mind and Healing Magic) that the spell distributes accordingly, and probably spills over to more members if it is able to top off the first two targets.

Personally, I wish I still had the old Curaga that hit everyone for 600ish, as I like to save Sacred Prism for Stoneskin. The only difference is now you have to choose between total AoE cure vs. SS, depending on the situation.