> ... none of this is “waste”. It’s already being stored or used.
Turned off wind turbines at times of surplus. They tell us that nope, it is not (yet) being used or stored.
> Finding new demand for it simply makes it more expensive for existing users.
It's not that simple. It could very well be the case that selling a portion of energy that otherwise has no demand to a buyer of last resort enables the business to be profitable. Not selling this portion of energy would mean that the operator would have to charge their other customers more in order to be profitable.
So it could in fact make things less expensive indeed.
Sure, there’s conceivably times of low demand when some energy would otherwise go unused. But a “ hydroelectric dam 1000s of km from civilisation”? Heat extractors in Vegas hotels? You’re imagining a fantasy world.
Further, what you’re ignoring is that none of this is “waste”. It’s already being stored or used. Finding new demand for it simply makes it more expensive for existing users.