Something that I would like to see is an improvement to the refining system. If the game is saying that I have a guarantee to get to +7, then my feed shouldn't be saying that it took several tries to get there costing me way more money than it should be.
Note if you are fighting the higher level ninjas then take all your armor off. The damage is multiplied by the amount of armor you're wearing, so if your armor is zero then the damage is zero...