After chapter 52, how has Pip changed as a person? What do you think is causing these changes in him? Is he simply maturing, or is more going on here?

Yes Pip has come full circle by ch. 52. He sees the illusion of being "gentry" and sees what he has lost in trying to obtain that illusion. Pip sees the truth and the truth shall set him free. Unfortunately for Pip, and many of us, it took loosing something beautiful before he appreciated what it was. Pip realizes this. Jo, his sister Jo, Biddy, Estella...were all people he had lost or grown apart from. Pip understood that money and status were no replacement for love.