Look at your traits, unlike treasure hunter you do not get MAB2, u just get MAB once in the menu. Each consecutive time you get a MAB, it increases the effectiveness of MAB. This is like dual wield and resist traits. You don't get new traits each time you get it, your trait is just improved.
Also, the trait says "Improves power of magic spells" for both rdm and blm. It does not say "Increases the damage of offensive spells." I hate to disappoint the allakhazamists out there, but this site in not all knowing.
Edited, Fri Nov 18 17:45:47 2005