I lurve Costco. You've already touched on the high points, but here are a few more you might not have considered:
1. The pharmacy and optical can be really good deals.
2. If you get the Costco Amex, you also get the added protection of the Amex on everything you buy with it, not just at Costco. For instance, I had purchased a Nook from Barnes and Noble 2 1/2 years ago. At the time I bought it I bought the additional 1-year extended warranty. Naturally, five months after the extended warranty ended the Nook died. American Express gives you an additional one-year warranty past the manufacturer's warranty or extended warranty on anything you buy with your Amex card. They also give you 90 day protection against theft and breakage.
Just to clarify -- you get the rewards from the AmEx on everything you buy, not just stuff at Costco, and you can use the cash-back rewards anywhere, not just at Costco. They'll send you check and you just take it to the Customer Services desk to cash it. I wasn't sure from your post if you knew that or not. ;-)
3. You can also get good deals on other services and goods. We got new carpeting through Costco. They subcontract it out to a local company. They also have a tire department where we get our tires. They do lifetime tire rotations for free and the tires are covered by a road hazard warranty. We got a couple of nail holes in one of our tires and they replaced it when they couldn't repair it.
4. They also offer discounted travel or special offers, like Costco gift cards when you book travel through them.
So anyway, when we started taking advantage of these additional services it made the executive membership a lot more valuable and we earn a lot more "rewards." The first couple of years with the executive membership we would get part of our membership fee reimbursed because we didn't spend enough there to make it up in "rewards," but now that we get more through them we usually get enough to cover the cost and a little extra.
Regards,
Trina