The Metaphysics of Poetry
One aspect of this interesting area of thought, which goes beyond the search for objective reality beyond the human realm such as the Forms, is states of consciousness. I think that this was touched on briefly in the thread you had several months ago on Julian Jaynes's, 'The Origins of the Bicameral Mind.' It is interesting how he maintained that ancient people did not necessarily think in terms of the clear distinction between inner and outer reality which we have today.
I also think that there is the issue of stepping into altered states of consciousness. This is touched by in the anthropological understanding of shamanism, but it also linked to what dimensions are believed to exist beyond the three dimensions, including fourth and fifth dimensional reality, and even the idea of parallel universes.
It is possible that states of consciousness can involve stepping into unknown dimensions of consciousness. This is touched upon by Bucke in his, 'Cosmic Consciousness'. His description of the development of specific individuals includes the Buddha and Jesus Christ, but it does include a number of creatives, such as Dante and Walt Whitman.
Of course, we are talking of people who were beyond the experience of most individuals, and the majority can only touch upon such inspiration through the works of these creatives. However, I do believe that the process of creativity, including the writing of poetry relates mostly to subjective experiences but it is interconnected with states of consciousness. The link is probably in the realm of peak experiences, such as described by Abraham Maslow. Sometimes, I think creativity can become mystified through consideration of great works of art, but I believe that it is possible for most human beings to experience some creative 'inspiration', especially in the context of some kind of peak experiences amidst the mundane aspects of daily life.