>> I have seen plants seem to take a harder hit when regular watering in a garden was changed to less regular.
I could easily believe that, though not from books. Plants that often have to scramble for water probably adapt by putting more energy into growing deeper roots and more root hairs. I have read that root fungi grow thicker on plants that don't have sufficient water or phosphate. They will scavenge what water does appear very efficiently.
Maybe plants that always have plenty of water (until they don't have any) lose some of their leaves' water-conserving ability.
If you have heat, low humidity AND wind, maybe a wind break would let your plants get by with less water. Is there any chance of giving them some shade that might double as a partial wind-break?
Someone mentioned the technique of using irrigation drippers (like dripline or drip tape, but laying it down UNDER the mulch. With your compacted, rocky soil, I bet that any scheme for "deep watering" that requires digging would be "right out".
