My two cents - I hope to add to the ad nausiam useless info on this subject:
(1) On the surface I agree with DrDeth and Polycarp - Plato made it his life effeort to teach his new, organized ideas and ethics through dialogues, stores, etc.
I would liken his efforts (for example) to those of Gene Roddenberry and George Lucas – describing an ideal super-government, and bad stuff still happens - and students/people learn from it. What did we learn from the ‘KRITIAS’?
[Plato's Critias]
---- That teachnology NEVER makes one more powerful than “the gods” and that even a super-culture can be destroyed by a simple natural disaster in “One day and one night” - essentially, “all good things MUST come to an end”. People of every country (even the US 
) should at least keep this in mind.
(2) Underneath, I will use Roddenberry and Lucas to reflect back on Plato – Roddenberry (Star Trek creator) and Lucas (Star Wars Creator) cannibalized many old myths and urban legends to make us feel more familiar with the situations and people, subconsciously, so that their point gets across more easily. I get the feeling Plato may have done something similar with the ‘Atlantis’ Story. The urban legend may have existed before him, briefly mentioned by parents and masters to their children to teach them about humility.
(3) A self-admitted solar calendar was not adopted by any large group until ~ 2500 B.C. or so, by Egyptians. Before that, most nomadics used imprecise lunar calendars and agrarians (Sumerians esp) were using regular astrological calendars to decide/detemine seasons. For anyone to claim that they KNEW Atlantis was around 9000 years ago is a bit like saying that you found a coin that read “15 B.C.” on it and you believe it’s real.
(4) If one were to go out on a limb and assume that the legends’ claims were based on an atequated lunar calendar, 9000 - Lunar cyles places it at about - 690 years or so before Solon’s experience. If we assumed Solon was within the lifetime of Plato, that would place the story told to him ~ 400-500 BC. Subtract 690 years and you arrive near the end of the Minoan civilization at ~ 1100-1190 BC, within a 1-2 hundred years of Thira blowing its top.
(5) Medi-terranean: In latin Medi = middle , Terra = world (Latin was much later, but you get the attitute of the peoples). To Aecheans (excuse me, I meant Aegeans), Thira and Crete are near the middle of the known world of the time. Plato’s story might well have played on the urban legends surrounding an old currupted empire’s sudden destruction. You know how people are - “if they were destroyed, they must have been BAAAAAD”, and so on.
Any way, I hope this adds to the mischeif.