Regarding: "So, if you wanted to take this approach to Odhinn winning the Mead of Poetry, you'd focus on how Odhinn changes shape, goes underground, meets a female figure, they have sex, he takes a precious liquid, and then changes shape to escape again, chased by a giant who has also changed shape. Now, clearly, the details of each of these steps likely have meaning (why does he change into a snake at first and an eagle at the end? Which female figure gives him what precious liquid?)"

My interpretation:
Odhinn changes shape = gets horny
goes underground = goes to woman's bedroom (dark chthonic place)
meets a female figure, they have sex = as it says
he takes a precious liquid = gets inspired as a result
then changes shape to escape again = no longer horny and does a runner
chased by a giant who has also changed shape = pregnant woman wanting commitment
why does he change into a snake at first = got horny
and an eagle at the end? = got inspired (mind soaring)
Which female figure gives him what precious liquid? = muse gives him inspiration