What does Joe offer Janie that Logan doesn't? Does she love Joe? If not, how is "the change ... bound to do her good?"

Joe offers Janie excitement and opportunity. He represents fancier things than simply being like a servant on a farm married to an old man. I think Janie is initially infatuated with Joe. He represents something new and exciting: an alternative to Logan. Infatuation and love are two different things. I'm not sure the change is good but it is part of her journey.