I have an ebay store. It is worth it to me, because I sell online for a living. I would only recommend signing up for an ebay store if:
1)You can keep up an inventory 100 or more items for sale
2)You have multiples of the same items to sell in a fixed-price format
3)You have at least some items that are unique on ebay
4)Many of your items consistently sell in the same price range
Listing fees are cheaper for stores...but store items do not come up in a general ebay search, unless the search returns less than 20 items.
If you have a store, you still need to run auctions to attract buyers to your store.
Final Value Fees are higher on store sales as well.
I have an inventory of about 500 items in my store at any given time. I still run 20-40 auctions per week on top of that.