I got a discount to Sams (different store, I know) and they gave me $50 toward my first time purchase. It paid for itself.
As far as either store goes, you have to spend money to save money.
Where Costco/Sams is a no brainer, if you have a big family or buy a ton of food.
Another example, Monster Energy drink. You figure at $2.50-$3 a can in a normal store or about $30 for a case (24 cans IIRC) Just buying that 2 times a year pays for the membership.
You have to shop smart there. You probably dont need 10 pounds of hot dogs or 1000 cans of green beans so the bulk thing can get annoying if you only want something small. If you are really good, you can plan your meals/food purchases out way further in advance because either store doesnt always have exactly what you want.