response to adena and mrs. kahan re: historicity of purim

Adena,
I found your question interesting and Mrs. Kahan's post very informative.
I think that whether or not Purim actually occured is not necessarily so important.
Chazal---either because a historical event occured that contained important spiritual messages, OR because they wanted us to inculcate such t messages into our spiritual personalities--established that we celebrate this holiday. There are a number of critical spiritual messages that emerge from the holiday of Purim: searching for and recognizing the sometimes hidden yad Hashem in our lives, the importance of the individual in taking a stand for the well-being of klal yisrael, the importance of doing what is necessary to go back to Eretz Yisrael to build the Beit HaMikdash instead of being complacent during our time in Galut (see tanach.org), etc. The point, I think, is the Chazal wanted us to have a brief yet intense period of time-taanit Esther + Purim-when we can focus on these ideas and process them and integrate them into ourselves. Whether or not purim happened, the opportunity to have this "focus time" and the means that Chazal gave us to do this (the mitzvot hayom of Purim) are an incredible opportunity for us as religious individuals.