Damn, that's amazing! And pretty helpful.
A quick search gave me limited help - any idea where I might be able to find good tutorials on how best to use this feature?
Parameter wiring is pretty straightforward thing in 3ds Max and pretty useful too. It's also easy to learn, i think i've read Max help on it, did a couple practice wirings and that's it. You probably can find some tutorials on YT if you want more streamlined experience. One evening should be plenty enough to learn it.
Does it work in reverse? So for instance; I have a slider; I change it and the geometry z scale changes). But if I manually change the z-scale of the same object, the slider responds?
Yes, it can work in one way, or another, or in both, you have an option to set up parameters relation to each other in parameters wiring window.