An eBay Store can be worth the basic fee of $15.95 even if you're a self-publisher with a single title. Having a store allows you to sell copies of your book at a fixed price, and you can offer discounts on slightly damaged or shopworn books.
Your eBay Store listing will also be indexed by Google and other search engines, giving your title more visibility on the Web.
Another benefit of having an eBay Store is you can link from your Store to your Web site or blog. This not only provides extra traffic to your site, but the link from eBay enhances your site's ranking with search engines.