I go to the Iwelei I costco about once a week.  Yes, the clientele are not the greatest but as stated the employees are great.  Walmart and Sam's have high turnover minimum wage workers that directly reflects their business model.  I will go to longs and local supermarkets only if I cannot get a product from costco or I'm in a rush.  

I just got a $300+ cashback check from the costco credit card that more than pays for their annual membership fee.  Some items may not seem cheap but normally it is because the quality is much higher.  To live a bit more comfortably in Hawaii I purchase most of my stuff from costco and amazon.