While there are other positions that need strenghtening more than the striker position. Why pass up the opportunity to buy a player that would significantly improve a not so good strikeforce anyway. At least you're making a position strong that way.
Buying someone for > 40m € isn't exactly an "opportunity" for me. You can pretty much do that every single season, if you have that much money.
And yeah, Aguero would improve our attack, as would Rossi. But why improving what's already decent in the first place, while spending as little as possible on other, more important areas?
The more I read this thread, the more I feel that people are massively overrating Aguero. Hell, this thread would make you think he's Messi & Ronaldo combined. Only better.
Personally, I really don't think he would be the difference between ending 7th or 3rd, as I have seen claims.