Tom,
Aesthetically, the bunkering on Scarlet was a negative during my time there in the 70s. Many were not placed in the ground at natural rises, built-up artificially on the flat terrain.
However, from the standpoint of function, I think that they worked quite well. The bunkering on several holes, nos. 2, 3, 4, 7, 9, and 14 from the bottom tee, have a huge impact on how the hole is played. And in my few hundered rounds there, I am sure that I visited every one on the course at least a couple of times.
I've only played a half-dozen or so MacKenzie courses, but his bunkering, while highly artistic and making a great visual impression, didn't see to come into play very much. Perhaps this has to do with these courses not keeping up architecturally with the new technology.
Funny that you liked the spruces. I think that the forestation of Scarlet, particularly with the junk trees such as the spruce and crabapple, detracted from the course greatly. The spruces in particular with their branches to the ground and planted on some of the turns just a few feet from the fairways added little beyond lost balls, delays, cheating, and fustration. Thank God they are mostly gone.
Let me know the timing of the work and perhaps I can schedule a trip up there to see the finished product. It has been some seven+ years since I've played Scarlet.