Does anyone know anything about how "money can't buy happiness" in this novel? Any quotes or insights?

Concerning The Great Gatsby, you
should be careful of looking for simple, easy one-liners in sophisticated fiction. 
Human existence is complex, not simple, and sophisticated fiction usually reflects
that.

For instance, in this novel, money is only a means to
an end for Gatsby.  He doesn't strive to become wealthy because of greed.  He strives to
become wealthy for the sake of winning Daisy back.  Money only matters to Gatsby because
he thinks it will help him win Daisy back.  An easy one-liner about money not buying
happiness doesn't apply to Gatsby.  Daisy will bring happiness to Gatsby, nothing else. 
That is the issue.

For another example, Tom is definitely
leading a happy life, so to speak.  He has a beautiful wife, doesn't have to work as far
as the reader knows, and has a girlfriend, too.  And he wins in the end.  He is so sure
of himself and so ignorant that he thinks he's always right and enjoys the winning.  He
has what he wants and gets what he wants.  If one wants to apply one-liners to the
novel, one could argue that the novel suggests that money can buy
happiness.  A reader's judgments concerning Tom do not take away from the fact that Tom
is happy with his situation and his life. 

The corruption
of the American Dream is at issue in the novel, as are one's ability or inability to
recapture the past, illusion, and other issues.  But saying that the novel shows that
money can't buy happiness is too moralistic and too easy and too simplistic.