After taking a short break from working on the terrain, I surprisingly quickly worked out a way of getting the references to work out correctly in Unity. As predicted, my mistake was actually generally pretty stupid, as I had done a re-declaration of the all-important variable I was suppose to be passing into my UpdateMeshVertices method. With one instantiated in the class and one instantiated locally within a private function, the class version was never edited, and was simply null as the private function the creates the first height map never had access to it. This isn't of interest to most of you, but I believe it's helpful to review it here.
Because I was using a sample from one of my poorly mixed, slower pieces that I wrote, the effects of the audio on both the original visualizer and the terrain were more difficult to see, so I switched it out with a sample mix I had lying on my computer from sound recording and production 1. It works!!!
Some of the biggest issues are obvious. The colored terrain is not pointless, as it'll be constantly changing, which is fine all of the terrain will end up being either ground or water. The other main problem is where the creativity starts to be required: the eight bands that divide the frequencies of the given sample work great, but they are static and two-dimensional (x-axis and z-axis). I need to start figuring out how to separate the bands (probably start with 64 bands) to make the arrangement 3 dimensional to make the terrain more water-like...