Should I divorce all?

I maxed out every badges and only gotten couple of keys for random characters but i have claimed more than 400+ characters which will give me 65k+ kakera. I would still keep some characters but should i divorce all to build the tower and invest in $kl? Or should i add more in my disable list and and aim for getting more keys of the higher rank character i have?
I got Hatsune miku and i just maxed her out in $op, so i am kinda aiming for her keys.
Whats the best strategy anyways?