Is there a point listening to people talking among themselves?
Short answer: No.
In FFXV this is equivalent to in past FF titles walking up to NPCs and pressing X to see what they had to say. It's usually just flavor text about the area or recent story events to make the world feel more alive. As far as treasure goes I haven't personally encountered a single case of this, however, in the story progression some NPCs give clues to where to go next.
As a side note it's possible to walk away and back to NPCs to get them to trigger a dialogue sequence, after a short while you will see they just repeat like past games.