Well she gets with her aw a 2% chance of assassinating an enemy and that's quite a lot for a unit that deals dmg to all units it blocks.
Sakuya is also not so bad, with aw she boosts Samurais and Ninjas attack for 7% by just having her in the team. What can be usefull, if you need a ninja to deal a good amount of damage. But that's still quite situational and in most times just a more-value setting.
So yeah no hurry in lvling them, but they can be nice.