In Part 1, we looked at Aguero's stats suggesting that he may indeed be worth a similar amount to Carlos Tevez. The problem is that this transfer is not happening in a vacuum and Aguero's value to Man City is very much related to whether Tevez stays or goes.
Let's imagine Tevez stays and Aguero is brought in. Assuming the want-aways (Bellamy, Adebayor) leave, City would then have four principal strikers: Balotelli, Dzeko, Tevez, and Aguero, all of whom transferred to City for over 20 million pounds with high wages to match those fees. Aguero, in that scenario, is just not going to provide enough value to justify his wages, let alone his transfer fee, because there are too few games to go around. He needs to be consistently starting to deserve the wages reported. Even if he does start, that pushes Dzeko and Balotelli to the bench and their value relative to their cost drops.
Plus, if Tevez stays, the club will have paid the transfer fee for nothing. At the moment, no other club is bidding for Aguero. It is likely that had City not stepped in, Aguero would still be an Atletico player. If we still have Tevez, why not wait until Aguero's contract runs down and we have more leverage when negotiating a fee with Atletico?
At this point, a Tevez move is looking less and less likely. City have shot themselves in the foot by resolving the Aguero situation before Tevez because now clubs KNOW City have to sell Tevez. Put it this way, that 50 million fee is not happening anymore. If we get as much as we paid for Aguero, we'll be lucky.