As an author of fiction and poetry alike I find myself qualified to answer this question. Does writing and publishing poetry help with the sales of fiction.
My answer, Yes of course.
If you have read my post Divide and Conquer – An Indie’s Strategy, you will know of my opinion on different ebook retailers and there is something similar here. Some people like reading fiction and some people like reading poetry so if you write both then you get more people reading your books.
Writing poetry can help express your creative side so it will actually help in the long run for writing fiction. I personally prefer writing freeverse poetry but you could try a limmerick or a haiku. Reading poetry could giving your inspiration to write a poem of your own on write some more of your latest story.
Poems are really short pieces of writing so you can write a lot in a short period of time. You can publish them individually or as a poetry book. People who read and like your poetry will most likely read your fiction and may recommend them to other people. You could upload an audio recording of your poem to your website and offer it as a freebie if you sign up to follow your website or sign up to a newsletter.
There are sites that publish collections of poetry like Randomly Associated Poetics into a e-zine and you could try one of those. There are also poetry competitions online and some are free to enter. If you have a blog you could use some of your poems and make them into a blog post. You could even invite other writers to contribute some of their poems to your website.
A great idea is to write a poem to accompany one of your stories. Like an audio recording you could offer it as a bonus or offer a paid version of your book in exchange for the poem and recording.
Good luck writing poetry