IIRC everybody gets the same drop, it's all just a %, no equips or anything you can do make the chances of X dropping any higher. As for mage combos? I really WISH you could use Magic Combos. And have an AoE combo with a certain amount in that element. But I'd say, don't try to make any combos for mages. Use the AC for stronger spells or Seeker.
PsN : Ryuu_Hyuga(M)-Zerou_Cool(2) (Mainly Playing: MOVE!) "PS Move makes the Wii look like an old school fat Gameboy with only 3 AA Batteries" ~ Me
Some kind of "magic burst" that gives bonus damage, like the way it was done in FF11 at the end of askill chain, might make magic in combos useful. But in WKC the usefulness of magic at the end of a combo is non-existant.