Tom,
I'll try to answer your questions in reverse order of your asking.
The bunkering at Prairie Dunes and Old Town was very site specific from what I can tell. It appears from all the early photos I have of many of Maxwell's courses that most of his bunkering was very simplistic. Most often oblong or oval in shape with somewhat of a sand face and tightly placed against the green. So I think though he was capable of this style he didn't do it on a majority of his courses, especially those early on in his career pre-MacKenzie. I've not really thought about his bunkering on his post MacKenzie work due to the lack of photographs at this point of that work. I only have photos of Old Town, So. Hills and PD to look at and I would like to compare other courses before saying those 3 are the usual. But that issue should be taken care of shortly and I could probably provide a better answer on the post-Mac influence of his bunker work.
I agree that the the bunker work at the course was all MacKenzie at the time that Maxwell came in, but his bunkering style at least what I have seen of it looks much more like what the modern version appears to be. I would love to see a photo of the work shortly after Maxwell completed it to see if it was done the same way. That may answer some questions and bring up some more.
As for the number of bunkers at Augusta, I think I read somewhere that MacKenzie admitted that this was an inordinately small number of bunkers for him. Though he thought many courses were overbunkered, the number at Augusta were much smaller than his usual work. I am not an expert on what MacKenzie's work originally looked like, but maybe he did use the ground contours to a much greater advantage than I was thinking before. I would love to hear some examples throughout the course where the contours themselves make a huge impact in the play. Maybe I am under the wrong impression about Macs work.