As for me, I think that Goku never really cared about saving the world in the first place, he just wanted to do his adventure and fight stronger foes. It just happens that in the previous series the earthlings are the casualty of those fights. Being a Saiyan explains everything there they live to fight and fight to live. True he may care but only to his close friends.
As the series changes, stronger foes exist his thirst for fighting increases more and more as well.
I think his personality had more layers in DBZ, because in Super he is more selfish and immature.