i'm having the same problem. YM networks is no longer paying good. each network is now totally dependent on what ad space they sell and all of them are bad but in the past before they closed the exchange they used other networks inventory so their rate was okay.
i'm looking for second tier networks which i really can not find.
currently i'm using second tier network space for cpa networks, it takes alot of work and at first you may get 0$ but i'm sure you will end up with better revenue than using any of YM networks