I guess it all depends which strategy you use to play. I quite like Athena as a striker too, so I don't always have her casting spells. Also Clochette has very nice boosting spells but they're quite expensive so reducing their cost in half was very helpful! Even healing is just 1SP now, so a very good bargain!
Plus Athena already has her "Concentration" spell which allows her to recover more HPs from battles but yeah if you use her spells a lot I guess it still makes sense.
Only one who can't equip it is Peeboo, if he could I probably would have tried using it on him... He's usually the one ending up with low SPs... I guess I like carrots too much!
