Perhaps it would be just as amazing now, but then again, I feel the time period does add a little bit to the impressiveness. For instance, back then most people thought lightning occurred because the gods were fighting. Today, we are much more educated and have access to much more general knowledge. As a result, you would expect this to leave people with more time to think about greater things such as the ideas in The Allegory of the Cave. Plato is impressive because he thought of it amidst a very unknowledgeable people.