WYSIWYG, I'm going to have to try your system of ever-increasing detail. Usually when I retell it the details get fewer, so this "other" trend sounds fascinating and useful. Also, who can yawn, the dream-teller or the adorable listener?
This works to the extent the listener is really listening and not offering to interpret, guide, etc., or rush to their own similar experiences. Eye contact, staying close enough to let the teller know someone is there, but not so close as to stifle the telling or shut down the teller.... if the teller shuts down the listener just leans back a bit to the popint at which the words were flowing well.
It's fine if the listener has NO IDEA what the teller is telling. If the teller is embarrassed about any of the content, it's fine to use made-up words in the telling, as long as the same words are used over and over. ("I dreamed I was in a dark alley, and a huge, scary "celery stalk" came up to me!" and so forth.)
Deep emotions may come to the surface, too-- it's up to the teller whether to pursue those and let tears flow, or whatever.
And yawning is always appropriate, for either party. When yawning occurs in this kind of situation, it's a sign of productive deep work being done; it's meaninghful to the yawner and it does not have to be analyzed or articulate-- just appreciated. Every yawn should be paid as much attention as one would pay to a delightful and charming child telling all its special secrets to a visiting relative. ("Good JOB!", etc.)