The stores are a great buy if you have a large inventory of items to sell - primarily becuase you can list them for nearly nothing (and you only pay the higher final value fees if you sell something from your inventory) - you can also avoid these higher final value fees by opening your own website and refering your customers directly to your ebay store from your website. With a large inventory this saves bundles of cash (that might be used to fund an account to advertise for your website). Do I recommend ebay as a good marketplace to sell items & generate extra cash, absolutely...it works like a charm. There is one downside to having an ebay store, your store inventory items get very little exposure...so if someone isn't searching for your extact item, they often do not ever see your item. So, many times you pay extra, because you pay to list the item as inventory, then you pay again to list the item as an auction. If you don't have a large volume of monthly sales - stick with a personal account, the advantages are not that great with a store...they are very affordable though.
Hope this helps.