I go back and forth on having an eBay Store. I open one, have it for a few months, get sick of it, and close it, then a few months later I open it up again. For anyone who is interested, this is a little chart showing the cost comparison for insertion fees for basic level Store versus just listing Good till Canceled listings without a store at all. The final value fees are the same.
As you can see, unless you have 55 or more listings at all times, you are better off to just list Good till Canceled listings without a Store. Beyond that, you start to save money with a Store. Added advantages to having a Store are the fact that you get 12 photos with each listing at no extra charge, which can be nice; and the big advantage of being able to put your Store in vacation mode any time you need a break, so sales cannot go through while you are unable to fill orders. One more advantage is the ability to run special sales in your Store, for dollars off, percentage off, free shipping, et cetera.
At present I don't have enough stuff listed to make it worthwhile, but I should list more anyway. I may reopen here one of these days.