This is more a methodological question. I understand that historical accounts come from multiple different types of sources, but I'm wondering what historical information, if any, is typically taken from something like the Iliad, the Odyssey, plays by Euripides, "historicsl" musings during Platonic Dialogues, etc.? Are there any ideas in those works that have been accepted as historically true? And if so, what criteria is used to separate out the artistic, the allegorical, etc. from the more direct historical accounts.
The Trojan war is an example, most of what we know about that is through poetic accounts, but it also constitutes in the minds of most people a historical event that unfolded generally in the way imparted to us. Yet I seem to remember archeological evidence popping up relatively recently that challenged some ideas about it. But as historians, how much do you take from the stories themselves to be at least relatively accurate?
In some cases poetry has the potential to tell us something about public attitudes to contemporary events; in other cases, poetry can be indicative of propaganda efforts. And the mere act of using poetry to celebrate something can be indicative of values that people wanted to see celebrated. Some examples:
A play like Euripides' Trojan Women tells us something about a subtext, at least, of Athenian regret for the genocide of Melos in 415 BCE. The Athenian assembly had voted for this genocide, but Euripides shows us something about the different, yet not necessarily violent, currents that constituted the will of the assembly at this time. As it turns out there was a short-lived oligarchic coup a few years later, which may in fact represent some of these undercurrents, but in 415 the fact that Euripides could publicly express sympathy for the Melians, and stress external causes for the genocide, indicates something about the freedom of public discourse. The fact that Euripides' tetralogy won second prize underlines that freedom.
Propaganda: the most obvious example is Simonides' ode about the Battle of Plataiai that effectively decided the Second Persian War. The nature of the poem indicates that it was for a public commemoration; and the central position of Pausanias and Sparta in the surviving fragments indicate Spartan sponsorship. This fits well into a narrative of Spartan propaganda campaigns throughout the fifth century BCE. In a more subtle way, Pindar's victory odes routinely use mythological stories as a backdrop to the person, family, and/or home city of the athletes that he's celebrating. In many cases these mythological references can serve as an indication of how that family or home city wanted to see itself represented in public. It can also help us date cultic and propaganda trends: for example, Pindar's 5th and 6th Isthmian odes, in honour of an Aiginetan athlete, celebrated the Aiakids, including Peleus and Achilleus; this can be linked to cult worship of the Aiakids on Aigina in the 480s.
Values: if you find a grave with a lengthy poetic inscription that celebrates the dead man as, effectively, a Homeric hero (as in the case of the inscription for Pythion of Megara, IG I^3 1353), you can infer that Homeric values have been incorporated to some extent into military discourse. If you find references to the Iliad in a poetic inscription erected in the Athenian agora to commemorate a battle (the battle of Eion, 475 BCE), that reinforces the point. Both inscriptions also attest to the popularity of Homeric poetry in Athens in the fifth century.
But when it comes to using poetry as a source for historical events, poetry is at best tangential, at worst outright misleading. It can never legitimately serve as a main source; it only gains value if it's corroborated by some firmer kind of evidence, and in that case, why bother with the poetry at all? This certainly applies in the case of the Trojan War: it would be crazy to infer a war fought over a kidnapped woman between heroes named Agamemnon and Hektor, in which the gods routinely stepped in to help heroes on the battlefield. Simply deleting the fantastic elements and taking what's left as history wouldn't be any help. Instead, we look at archaeological evidence and Bronze Age textual evidence, and if we find correspondences in Homer, then there's something to talk about.
Even the Hesiodic Works and Days has doubtful value for the history of the Archaic period, even though it is a contemporary poem expressly about cultural practices of that period, because it is so transparently an attempt to paint a very particular kind of picture of that society. Hesiod paints the position of basileus in much the same way as Homer, not as an aristocrat but as a kind of big man who exercises influence by his personal qualities and leadership skills, and whose giving and receiving of gifts is integral to his position; but it's very doubtful whether historical basileis were like that.