Yes, I do think the "Door" etc., and indeed quite a lot of the early chapters, were rather heavy-handed, but I also think it was probably intentional. Whether the reader finds it amusing will, of course, vary with the reader.
There were similarities between the ghost and the Ancient Mariner - at the very least the lugubrious (more with the heavy hand
) tone, and the demanding that others hear his sad tale - and there may be more if you bother to re-examine the work. I wasn't familiar with
Kubla Khan anyway, so may have missed some elements of that. I hadn't even remembered it was that poem that was unfinished due to interruption, so the punch line delivered in the book didn't quite have the effect that might have been expected.