I think we need to invest in an SS now seeing as DP retires at the end of the season. IMO it's our biggest priority as long as signing a LW. Yes we do need a CB as well, but I think we are relatively stacked in that position (Chiellini, Bonucci, Barzagli and Sorensen)
If we assume that Iaquinta/Amauri/Toni will also be gone at the end of the season (EDIT hopefully the first two gone before the start of the season), that leaves us with two strikers if we don't sign Rossi.
I'd love Aguero here, but if we sign him I worry that we will buy cheap/shit options for LW and CB. Whereas if we sign Rossi for a cheaper price we can get bettter quality in those other two positions.
And before anyone starts to label me a Rossi fanboy or some other shit like that, I'm not. I'd much rather Aguero here and think he is a superior footballer, but let's be realistic. This club wont spunk 45M (plus his massive wages) on one player.