> Get a robot vacuum or a couch or a VR headset for $100 off and your membership's already paid for itself that year

I think one danger with Costco is that it encourages overconsumption. It may feel like you're saving money - but you'd save even more just not buying a robot vaccum or VR headset.

If you do the research and decide you would benefit from a robot vacuum, compare different models to decide on the best fit for your needs, and then check prices at different stores and find that it's cheapest at Costco - then yeah I'd say you're saving money. But I'd venture to guess that most robot vacuums are just bought on impulse during Black Friday sales (for example) - which I don't think counts as saving money even if you get a big discount from the MSRP.

To be fair, this isn't a problem unique to Costco. I'm guilty of buying a lot of junk on Amazon.