I currently use the Gramary cape, and through my 50s I have noticed an increase in less resisted elemental Ni spells. Though slight it, allong with food and subbing RDM I have kept my ninjitsu dmg above an average of 60dmg per spell. Considering my katanas deal 15-25 dmg per hit, for a total of 30-50 dmg every 5 seconds, I still do more dmg with Elemental spells then with katanas. For those how are interested in using the elemental spells for dmg, the target dmg against mobs is 80. You should find that with resists you will do 60 or less on resisted attacks for a collective dmg of 400+ every 30 seconds (45 seconds if you are tanking).
I have found a series of items introduced in the new update (this item included) that give either magical accuracy or magical attack bonus that help ninja maintain the usefullness of their ninjitsu well into the 70s (I don't know if you would have to sub a mage job, or if by simply focusing on these you will stay above the mobs Magical defense).