Maybe I just dont rate him as highly as some on here. For me he is probably a slightly improved version of Nani - and im not convinced that he wouldnt suffer from the same inconsistency that Nani has done
If we did sign Sanchez then I think one of Rooney, RVP or Mata would have to leave, in addition to the current potential/expected departures (Hernandez, Valencia, Nani, Young, Kagawa - not all of them but I imagine some will go this summer).
Given that we will be playing far fewer games next season, we cannot possible keep such a big squad as we have done previously, and expect to be able to keep everyone happy. I wouldnt mind seeing some of the above (Hernandez, Nani and Kagawa in particular) go out on loan to good clubs (the likes of Everton or Spurs) next season, build up some form and gametime and then come back for when we [hopefully] are back in the CL, to bring the squad numbers back up.