I find your question highly insightful, because on the one hand this poem seems to represent a highly vivid yet incomprehensible dream which really defies explanation. Thus one view to take when studying this poem would be to argue that it really presents us with a series of fragments of the dream that Coleridge famously had and then couldn't remember. However, some critics would argue that in spite of this apparent fragmentary nature of the poem, there exists an underlying unity of purpose and theme that clearly shows the fragments work together as a whole and provides a structure linking them in to each other.
It is possible therefore to view this mysterious poem as a poem about the creation of poems. In fact, the poem itself has been created from air - with words - to give us vivid images and a new way of looking at creativity and the imagination. This poem then represents a celebration of the imagination by focussing on what Kubla Khan built, but it also reflects the danger of unbridled imagination, as summed up in the "tumult" that exists outside of the imagination's "pleasure-dome". Certainly for me a key passage that seems to sum up this theme and the desire and frustration of the author to be creative is the final part of the poem:
And all who heard should see them there,
And all should cry, Beware! Beware!
His flashing eyes, his floating hair!
Weave a circle round him thrice,
And close your eyes with holy dread,
For he on honeydew hat fed,
And drunk the milk of paradise.
The act of creation achieved by the author in building the "domes in air" would make him feared and people would regard him with awe, much in the same way that true poets who are able to harness their imagination are both feared and respected.