But then I'd miss out on the 4% back from my Costco Visa for that gasoline. And even _just that 4%_ pays for the membership in my case. :D

(My next-best card in terms of rebate on gas is 1.5%, so assuming an additional 2.5% from Costco, I need to buy $2400 in gas to have the full membership covered by just the gas rebate - not even counting the additional savings from the lower price of gas).