If you have mostly auctions it's not even necessary (or worth the money) to have an Ebay store. This is JMHO, so please don't anyone get mad at me
but it's always seemed to me that an Ebay store would be more useful and economical for folks who have hundreds of items for sale...with a store, they can sit there for a whole 30 days with a Buy it Now. The downside is that store items are not easy to find, but auctions are. When I sell, I usually have 25 to 150 items running at once but I've never seen the need for a store because I know I'll get more exposure with auctions. It all depends on what you sell, how much you sell and how you have your listings set up...personal choice.
Remember, JMHO