Unlike those of us who shoot in colour and then convert to B&W in LR, your capture of monochrome raw files is much closer to the traditional B&W film experience. With colour files, we can decide in LR that this part of the image should renders as a light grey or another colour is rendered dark. While you can improve the picture by dragging a slider or applying a curve, that B&W tonal conversion has already been baked in the raw file.
That means the key is to change your glass filter to suit your subject. Orange is mid way between red and yellow will allow you to render blue skies as quite dark grey tones and lighten up red rock and sandy landscapes, and I'd suggest green might be next as it will allow you to distinguish more tonal contrasts within foliage and other greens. Then red and yellow, maybe not blue ( I'm not a fan of pale skies or making white skin darker and rougher).
See if you can track down a copy of Ansel Adams's The Negative which has a chapter on using filters to fine tune the B&W capture, or his Examples: the Making of 40 Photographs. Also experiment with your in camera filters as the JPEGs will let you see how to use of glass filters proactively - your cactus scene in the different red, orange, yellow, green, blue filter versions would be a great example.
John
(and sorry if you already understand this stuff)