We need that "special" SS to make that leap in quality in Europe. Serie A isn't and shouldn't be an issue for the foreseeable future, seeing as we are at least a decade ahead of other teams in terms of having our own stadium, marketing, finances, etc...
Our defence is arguably the best in Europe (9/10), and our midfield is probably 2'nd to only Barca (9/10). Clearly, where we need upgrades is the forward line which I rate as a 6.
Chiellini, Bonucci, Barzagli, and with guys like Caceres and Marrone coming off the bench (maybe recall Masi or Sorensen) is a very strong CB department. Licht, Isla, Asmoah, and Peluso for the RWB and LWB positions are good enough. We don't need to spend too much on a bench player, or splash 20+ million to replace Asamoah in a position which he has so far excelled in (even though it isn't his natural position).
For the midfield, we have Vidal, Pirlo, and Marchisio, with Pogba coming off the bench. Verratti would be great, but he isn't a priority just yet, and I don't see him leaving PSG after only one season. Let's not forget that both Marrone and Asamoah can deputize in midfield as well. We have both depth and versatility in abundance.
Alas, we come to our forward line. Llorente on a free was a very good buy (only time will tell whether it will turn out to be great). We have Matri, Gio, Vucinic, and Quag. Bendtner and Anelka are likely to be shipped back, and Cackinta's contract is finally due to expire, so he can go and graze somewhere else. Vucinic is untouchable, and one of Matri or Quag will stay. Matri looks the more likely of the two, and we should get somewhere around 8-10 million for Quag (or use him in some deal). Giovinco will probably stay on for another season, but if he stays here next season, he should be nothing more than a rotation player and 3'rd choice SS. Hence, we need to invest and buy a Jovetic/Sanchez or Suarez/Benzema is the opportunity presents itself.