If this was the singular form any savvy restaurant owner in SA would love to own SanAntonioRestaurant, you don't have the .com but the .net is the next best thing, ie there are tons of great restaurants there, some of the best Mexican food in the US in fact, it's such a big city so anyone should like to have this domain in singular form (end user) and advertise his own restaurant as the one to go in SA, on top of the actual restaurant name domain. With that you could do cold-calling and offer it to a bunch of restaurant owners
But as she said, the plural does not work for that, it's basically just for regional search and general SEO potential is uncertain. If you don't see much promise in that then just send it to auction w/a min bid you're comfortable with. I have, with names that had limited potential, I even got a few surprises