This is a good example of how to do things. After a murder attempt by a poltergeist, a lovely female ghost asks for the player's help to break an ancient curse. A while later, after uncovering an old book and losing it to the poltergeist, the player learns that his failure to steal back the book will mean the end of the world. So, gradually upping the ante on the character can certainly make things more interesting. At first the player is driven by greed, but after an attempt on his life, something more powerful is needed, so you add a supernatural love interest.
Nobody has just one defining, all-consuming trait.
People aren't just records playing the same track over and over. Just because an NPC helps out the player in one spot doesn't mean the NPC always has to help out. Maybe the NPC only helps the first time because he mistakes the player for somebody else, or expects a fee in return. Even if he is doing it out of the goodness of his heart, that doesn't mean he has to go around doing good deeds all over the place. Not all good guys suffer from the Superman syndrome.