Definitely. SD County should do this, and all the other California coastal cities. They benefit from being near the ocean, therefore transport costs are reduced making it a win over importing.
For inland california, this isn't the case since pumping costs don't make it so clear cut cost wise. Reclamation efforts like the OP company, are a really big deal because they are one of those rare "easy-wins".
If San Diego needed to then they probably could, but this is generally one of the most expensive options. It is politically impossible, but it would probably be cheaper to pump water from the Klamath to San Diego than to extract it via desalinization.
For inland california, this isn't the case since pumping costs don't make it so clear cut cost wise. Reclamation efforts like the OP company, are a really big deal because they are one of those rare "easy-wins".