1st season, Tevez as one of the key players helped Man Utd to win the Double, including the CL that Fergie has been waiting for 9 years since 1999 to win that again. Fergie was the happiest man in the world.
2nd seson, Tevez is not really a happy man as 1st season but still make some impact in helping the team to win the PL again. CL will be next then. Fergie is still very happy.
So, what more can you ask of him to contribute so that to convince you he has contributed "so much" already? Triple Crown Champion? :D
Of course the contribution of the veteran Giggs, Scholes and others are unmatched and because of their dedication and loyalty I like them. But there is no point comparing the veterans to the "newbie" Tevez about his contribution to the club.