Even through traditional publishing, a writer has to listen to an editor. There are brainstorming sessions, recommendations, rewrites, and revisions. If you think self publishing should be any different, you still have some learning to do.
Self publishing is all too often seen as an easy way out in the cut throat world of rejections. While the marketing and such is slightly different, the basics at the beginning are pretty much the same. In order for the book to be marketable, the story must be solid, the characters believable, and grammar must be concise. If it isn't, you'll find yourself as frustrated with the results of the sales of your book as you were when you were getting rejected by agents and publishers.
Just because you've been writing for years doesn't necessarily mean that you're qualified to be an editor. And even if you are an editor, you shouldn't really trust yourself when it comes to your own lengthy works. You created the work so you will be biased about it. Having an intimate connection with the work will cloud your judgment. Hiring an editor will allow a professional to view it with fresh eyes and he/she will be able to give you honest feedback.
Self publishing should go through the same steps that a traditional publisher would do in order to give your work a fighting chance out there.