I've wasted 180 seals in sage for Naruto, now I don't even use it. But lucky me, I guess. I've got Darui, Chojirou and Mei for less than 180 seals in kage :lol
So my word for you, YOLO bro. Don't wait for seal rebate, if you happen to pull a good kage then by the time rebate come that ninja already help you gain tons of seal by winning battles.