What are the positive lessons of the Holocaust that Elie Wiesel hints at in Night?

One positive lesson is that the Holocaust allowed some people to value their family more than they did before deportation.  Elie's relationship with his father is not the best is could be.  His father sees him as an immature boy, and Elie sees his father as oblivious to what is happening around him. By the end of the book, Elie has taken responsibility for his father and most certainly is closer to him before their camp experience.

Another positive lesson is that Elie gains an immense amount of self-knowledge during the Holocaust.  He learns what he is capable of and that exacting revenge (such as the freed prisoners immediately hunting down their oppressors) doesn't usually help someone heal from a horrific experience.

While Elie learns some valuable lessons from being a Holocaust victim, one must still argue that those lessons could have been learned without his having to endure such awful circumstances.