Probably referring to that her voice sounds sweet or nice.
Explanation:
When you refer to money, you think of riches, nice things and all that. When Gatsby says that Daisy's voice is full of money it sounds very valuable. Most likely you'll get good, positive vibes.
a point of view and a viewpoint are essentially the same thing. They both refer to an attitude or a way of thinking about a particular subject, e.g. Try looking at things from a different point of view. Try looking at things from a different viewpoint.
