Not trying to put a dampener on everybody's excitement, but imo:
I can't see Dzeko being available. Wolfsburg won the Bundesliga today and unless he is replaced by someone better, I hardly think he will leave with CL next season and all, unless its to a bigger club already in the CL. Would take a massive offer I'd expect for us to get him, and I don't really know a lot about him. Has looked good when I have seen him a few times though.
If Benzema goes anywhere I doubt that it would be to us. United have been sniffing around for a long while and the other big clubs of Europe will be forming a long line for him if he was to be available. Would be an awesome signing- but again hard to see him coming to us when he'd have a many options for CL football, and plenty of cash that would be willing to pay OL plenty of money for his services.
I'd love to get Villa. I think he is a cracking player, but all indications are he wants to stay in Spain. But with Valencia's financial problems, he might not end up with a choice and so we could have a chance with him (I feel Silva may be more likely though)
Aguero. I think he's probably our best hope out of these four. He is still only young and may not yet want to go to a big club. We can offer plenty of cash, and we seem to always do alright when dealing with Spanish clubs. He looks a fantastic player to me. He is the one that I hope we are really chasing hard.
And Supercity, would you really play Robinho on the RHS of midfield? If he has to play in midfield, it either needs to be in the hole behind the striker, playing off the striker or on the left. We have players to fill that role, we don't need to be putting a square peg in a circle hole.