I avoid using Mobipocket Creator now because it seems to me that it is rapidly becoming redundant. For example, in trying to learn the ropes of ebook creation, I read that Amazon had increased the acceptable file size for in-text images but, as far as I'm aware, Mobipocket hasn't (and won't?) be upgraded to allow for this.
The system I am currently using is to create an xhtml file, edit it in Sigil (which I have found extremely beneficial), and then convert the epub to a mobi via the Kindle Previewer. The latter is extremely useful for testing how the books will look on the various versions of Kindle as well as iPad (iBooks) and other devices.
In terms of poetry, as DiapDealer pointed out, in Kindle books you don't seem to be able to apply a left margin to the entire poem AND have hanging indents, so I have settled for sacrificing the former. The hanging indent can be created by applying a left margin to a paragraph (or line) with an equivalent negative text-indent. To indent lines I've been reduced to using non-breaking spaces. It may not be pretty, but it works.
The code that you provided earlier in the thread is a neat way to handle poetry in epubs, and the good news is that it is supported by Kindle Fire. However, in the meantime, whilst most of the Kindle devices don't support certain code, I have to manually alter the original xhtml document and use a different stylesheet to create a second epub that can be converted by Kindle Previewer to display well on the various devices.
Finally, I should say that this forum has been of enormous help in resolving the difficulties I have faced.