According to Bava Kamma 79b, the penalty difference between a ganav and a gazlan is that the robber does not disrespect Hashem -- he commits his crime in full view of anyone, man or God but the thief hides his action from man (showing he fears man more than God).
Is there a parallel distinction made when assessing the reward for performing mitzvot? If I obey a mitzvah only publicly is it "worth" less because it shows that I am driven by man's opinion more than God's? What if I perform it in public and in private but only out of respect for another person's sensibilities and not because Hashem commanded it - would the "reward" be any different? Could there be a difference even in whether someone is yotzei through his performance if the motivation is not driven by Hashem?