Store has an advantage if you are listing your items as BIN.

Insertion fee is 20c for 30 days for most of categories and FVF is 7% which lower than one without store.

Books, Music and Movies categories has 5c insertion fee and FVF is 9.9% which higher than one without store.

The posint to consider here is the fact that BIN items won't show up in search in order of ending soonest in the best match search. So BIN listings can be sitting on 24th pages for 30 days if it's in popular categories.

Auction listings will show up in order of ending soonest. So Auctions will have more chance to be seen by buyers.

Auction in store will cost as same as non-store owners and store owners won't get 30 free listings whether they are powersellers or not.

If you are not a powerseller, using 30 free listing first to see how auctions go is a good idea before considering opening a store.