Nani at the end of the season and Valencia for most of the season were our best performers - no reason to think why that is going to change this coming season.
On the other hand, our weakness in big games was our control in the middle of the park. The lack of ability to retain possession under pressure and for the most part compete against stronger / more technical opposing midfields. I would put signing a player like Bastian Schweinsteiger as a higher priority than Ozil at this point.
His play in the CL, play for Germany letting the attackers do their business by winning possession or retaining it and yet able to also contribute in the attacking 3rd as well is precisely what we missed last season.
Though would mean getting rid of maybe one central mid as with Scholes/Carrick/Gibson/Fletcher/Hargreaves/Giggs - we seemingly are overflowing.