Are there historical sources available to answer this question other than surmise and inference? Tom Naccarato has a post on bunkering at the In My Opinion section of this site that gives a tease. He quotes J.H. Taylor at length about bunkering, and all of Taylor's thoughts go to issues of fashion and shot values, not water. There must be many other sources, some more directly evidential than this.
My sense is that the classic courses used extensive bunkering for reasons unrelated to water issues. Many of these courses did not have the trees they have today (even after recent tree removal) and the sand was necessary to give visual shape to the holes. It was also a big factor in the overall aesthetic of the course, in the low tree era when much of the course was visible from various standpoints. Plus this was a time when maintenance was less obsessive. Old photos prove that, as do the instructional books of the time, which favor long irons off the turf in all but the best of lies.
This is a different question, though, than whether tightening the water spigot on contemporary courses would result in more sand because of less fearsome rough. It probably would, and the grooming of the sand might get less persnickity. Then again, maybe not--they would just do like Augusta and make the speed of the greens (and maybe the fairways) inappropriate to the slope of the land. This for the pros, anyway. For the members, who knows, as most members would have a stroke (cardiovascular variety) at the type of course conditions that obtained in the classic era.
Interesting questions.