Why would you need to change mood for every ninja?
I have 4 ninja who I always use, I got them the moods I wanted and upgraded it.
There is like another 3 or so ninja who I use in some situations, like in group instance so I got them the lowest one, but nothing forces you to upgrade mood for every ninja, not even for ranked, because as long you dont max it, it wont make big difference.
Btw last Treasure Key event, you could get meat * for almost nothing and actually 20 of them.
What should be enough for some ninjas without buying any, especially iif you ad some more from the fishing event too.