No experience on restoration, but I've whacked a few birds at my parents place, and food and habitat is esential to keeping them arround.
My parents live on an old farmstead in North Florida, sorounded by fallow fields, the climate may be simalar to yours. Mild winters no spring or fall to speak of and summers range from hot and too wet to hot and too dry. They mostly nest in blackberry brambles, on the edge of fields. The brambles provide food and excelent cover from predators, and they can slip into the field, and forage for seed and bugs.They seem to like tall wild grasses, rarely seen them in food plots.
They like all fruit but, the best forage I've ever seen for quail is fig trees, a few fig trees can provide dead fall fruit for two to three months and draw flies for a month after. I've often seen them too fat to fly, after gorging all morning, below a fig tree. You can literaly scoop them up with a net.
But, that kinda takes the sport out of it.