Goodman Games

Idea which might be horrid/unbalanced/too restrictive: perhaps you want to choose to only give Luck to players with less than their starting max - i.e. burn some in order to get some back. Maybe raise this award cap by 1 per level for all players so that thieves/halflings can't ever get more than +1...

It also occurs to me that the problem isn't so much the color spray nor even the staff (although this to me, seems like spells that give permanent bonuses like enchanting potions, scrolls, staffs should not be rolled for but tied directly to level or some such with a "yes you did" roll or ...

Have you considered a small house rule? Each time the spell succeeds, a cumulative -1 penalty on the same spell is applied. Restoration of the negatives could be 100% next day after sufficient rest (bed rest, possibly only 50% reduction if not resting in a proper bed, etc.) or +1 restored per hour. ...