You're right, Dzeko wasn't exactly pulling trees up at City. To be fair though, his primary role was to play the foil to Aguero and was the 'out ball' whenever their defenders had to hoof it downfield. He has a good pedigree as shown by his stints at both Wolfsburg and Roma, and is at a good age as the perfect stop gap signing.
As for Cavani, it's more a semi-realistic pipe dream. Seems like he's always linked with a move away, and the guy doesn't exactly avoid the rumors going so far as to state that he'd like to play in La Liga or PL some day. I actually think Cavani's going once they sign Auba. The only question is whether he'll stick around for another year to play out of position but still get his paycheque, or if he'll demand a move this summer.