I don't know. The wages argument holds true; Man City pay ridiculous money there. Getting Bony in, who has been a very good goal scorer in the league for over a year, to me seems like a sensible move. They know Aguero is injury prone, that Jovetic is injury prone too, and that Dzeko isn't very good. Signing Mangala was an attempt at strengthening their core, and I think he will turn out to be a class signing for them, but it was difficult to predict just how shit Kompany was going to continue to be. He is their captain and spokesman anyway, so he is pretty undroppable regardless. I saw Fernando a few times when in Portugal, and he looked really impressive. It was difficult to gauge that he would have such a difficult time to adapt to the PL, and that he and Fernandinho would be such a poor pairing.
All in all, they signed exciting, promising, young players in Nastasic, Jovetic, Balotelli, Sinclair and Rodwell. They were very highly sought after players, possibly Sinclair excluded, but neither of them have managed to kick on. They signed dependable, classy players like Milner, Silva, Nasri, Fernandinho and Dzeko too; they have all done a pretty good job for them, but it is only Silva who has managed to really elevate his game a level IMO. Then there is Yaya, and there is Aguero. Those were superstars when they arrived, and they have delivered.
There are certainly a few flops they have signed too, but every club has them. Perhaps, they should have looked to sign a few more ready made superstars in the Yaya and Aguero bracket, but those players are hard to sign for every club. They tried to sign RVP, but he didn't want to go there. Perhaps that is part of the explanation here; not many top class players have been interested in going there, and they have had to shop in second best bracket.