Back when most people had heard of them we used to use proverbs to assess concrete vs abstract thinking after brain injury. eg "What does it mean when I say 'A rolling stone gathers no moss"? A concrete response would be "the moss gets scraped off when the rock moves. More abstract would be "If you don't stick to one job you'll never get rich." or "New experiences keep you from getting stagnant." The meaning was less important than their ability to move from the concept of the physical object to using it to represent a non-physical concept. It was not unusual for someone familiar with the abstract meaning prior to a brain injury to be unable to make that move after.
We don't use them much now not because people are more concrete (????) but because they aren't haven't heard of proverbs.