[6stringmerc]

Not really. Copyright in the US at least permits a base-level of protection, and should domestic or international plagarism occur, then having the original file(s) and correspondence would be excellent evidence. 'Copying ideas' like gets brought up often in lawsuits against movies are essentially non-starter cases. Ideas can't be copyrighted, simply the telling of the story.

In my circle of people, self-publishing is simply still a 'vanity' project and commercially not viable.

Being part of a reviewed, curated, and edited publication benefits the writer and reading public much in the same way that certain record labels (ex: Hospital) release materials that fit within their mold of quality.