I would say that we need to accept the mediocrity in the current lot of spinners (Few young ones might be hope for the coming future but, they are some seasons away) and try to compensate it with something that we have and that is spin bowling all rounders/spinners who can give lower order runs. Unless Yasir is in full fitness and form lets stick with Nawaz, Gohar, in next season or so Mubasir and push Shadab to improve fitness and play red ball cricket as atleast they can contribute in some other aspect as well while not being much of a downgrade from the current options.
There is Abrar Ahmed, Ali Usman etc unless are top quality spinners who can win the game on their heads wont add more to the game then the ones I have mentioned.