In my experience demos are half about the product and half about the team / company behind it. So I wouldn’t call its value zero: part of the reason a potential client is asking for a demo is to see if there’s actually a real, intelligent company behind the product.
The sales pitch needs to compete with other pitches, so I gotta imagine in a vibe-heavy market a solid sales team is gonna lead with all the stuff you can’t vibe.
Customer transaction numbers, service response times, human staffing for VIP customer service, and human engineers who are recognized domain experts. The cliche live call to customer support with some hairy-ass customer specific problem.
Plus vibe-upselling of vibe-integrations for whatever Wonderful Engineering the customer has with your profit centres.