...and to follow up #8, Aristotle certainly held prominence in Western Civilization for two millennia, not only laying down what would be incorporated into Church doctrine, but establishing views of the physical world pertaining to physics and medicine. Perhaps Plato's greatest legacy was Aristotelian Logic!
Someone once said that the whole history of western philosophy is a series of footnotes to Plato. In other words, Plato made so many important arguments that many later philosophers have spent their careers trying either to explain, support, refute, and/or elaborate upon some of Plato's ideas. His own student, Aristotle, often disagreed with his teacher, but it is clear that Plato stimulated the thinking of Aristotle and of just about every later philosopher who has ever read Plato.
Plato's most enduring influence has been in religion. His notion of the separation of the ideal world from the physical world has been influential to Judaism, Islam and Christianity, where St. Augustine popularized his thinking. As a political philosopher, he was among the first to describe the degeneration from an ideal state that would occur without virtue- a theme that has resonated throughout western thought, including, as historians have shown, the Anglo-American political tradition. His epistemology has not been all that influential since the scientific revolution, and particularly since John Locke's treatise Essay on Human Understanding.
Plato is often called the father of Western philosophy, and certainly his philosophical ideals have done much to shape Western philosophical thought and how we approach the world. In particular, an analogy that is rightfully very famous is Plato's description of a cave where the inhabitants have a skewed perception of reality. This led to it being used as an allusion in Jose Saramago's novel The Cave which argues that a similarly skewed perception of reality characterises our lives today.
Politically, Plato believed in the idea of the "philosopher king." He thought that some people were simply more capable than others and that those who were more capable should be given the ability to lead. He thought that this would be the best form of government. I don't think that we can really say that he had much of an effect on Western political thought. He is certainly no democrat and not in favor of personal and political rights.
Plato is one of the most important figures in western civilization. There are so many ways this can be seen. Let me give you one important way. Early Christianity was greatly influenced by Platonism and this shows in the Western spirituality. For example, there is a not really an emphasis on the value of the body. At times this lead to odd practices, such as asceticism. This is all from Plato who believed the body was a prison house of the soul. This particularly noteworthy in view of the New Testament's emphasis on the goodness of the bodily resurrection.
Then I don't really understand post #3.
Post #4 basically is saying that Plato a greater impact on western spirituallity than in anything else?
Did Plato have any politically influence on Wester Civilization?