Let's all not forget how bunkers started, as natural erosion from sheep bedding down in sandy soil on the links courses of Scotland. Bunker "hazards", IMHO, should be natural occuring hazards to the play of the hole. Any golf course that does not have a natural sand soil profile should not have sand bunkers, but some other form of hazard for the hole. Each golf course architect, golf course site would have to determine what will constitute a naturally occuring hazard for the site. Which is why I like the idea of maintaining natural streams, rock outcroppings, ponds, native vegetation, etc. to compliment the golf course by laying out the routing around and/or adjacent to the holes. Sand bunkers only exist because of the natural tendency of sheep to get out of the wind and rain on a sand soil links course.
To answer the question of maintaining bunkers. I like the idea of very large strategically placed waste bunkers, only maintained by the maintenance staff as needed, with a mechanical bunker rake without smoothing rakes and only using the vertical tines and scarifier to maintain a vegetation free hazard, no rakes for the golfers.
Troy