Thanks, that was it.
Installing the "x86" package for 2013 was the solution.
Job had the solution earlier, but he accidentally linked to 2012 instead of 2013, and when that didn't work I was afraid it was going to more difficult.
It didn't really sound like reinstalling iClone would be the fix, but it's really weird that this "went away." I don't recall purposely uninstalling any software in the last 6 to 8 weeks, so why was I able to install the "Total Plants" (Speed Tree") module before, but not again now?
Ahh... Do you suppose Reallusion updated their installer? That would explain several things. a) Why Job linked to a "2012" download as the solution, because that probably did fix it before, b) Why it worked for me the last time I ran the installer, and c) Why the "2013" download was the solution I needed.
Anyway... I get the installation prompt when doing the iClone "Substance" installation now.
Thanks, guys. You're the best!
iClone 7... Character Creator... Substance Designer/Painter... Blender... Audacity...
Desktop (homebuilt) - Windows 10, Ryzen 9 3900x CPU, GTX 1080 GPU (8GB), 32GB RAM, Asus X570 Pro motherboard, 2TB SSD, terabytes of disk space, dual monitors.
Laptop - Windows 10, MSI GS63VR STEALTH-252, 16GB RAM, GTX 1060 (6GB), 256GB SSD and 1TB HDD