You're confusing hype with the amount of times he is mentioned in the press, which has obviously gone up over the last 6 months with Udinese's surge into European places, but that should take nothing away from his performance. The ability is there to see, and he would certainly be a huge asset to us on the pitch.
Sanchez is more than a promising youngster as far as I'm concerned, and if not for playing in Udine, would have received more plaudits by now. He has grown as a player and is no longer the mindless ball hog he was at the beginning of his career in Italy. Even physically you can see a difference. He has put on quite a bit of muscle, like Pato, and I'm serious when I say I hope we give him a drug test if he signs.
As for being a fancy winger with no end product, 12 goals and 6 assists suggest otherwise, although it doesn't really do him justice, as he is involved in so much of their attacking play, despite usually being harassed by 2 players.