From what I can tell, the fan is the only part of the system that is working properly.
It spins freely by hand, spools up fine when battery voltage is applied directly, and the resistance is within the specifications in my repair manual. If the high speed circuit blew a fuse (the 30 amp circuit where the fan was directly connected to the battery), I'd suspect an issue with the fan itself.

As for what caused the initial low speed relay to quit, I don't know. I've been less than impressed with the electrical system in general on this car. The fuse blowing on the low speed side was due to the failure of the inline resistor. It likely has a crack internally and overheated. When these types of resistors are overheated, they momentarily have nearly a direct connection (the resistance drops for a second) right before they die. This is what I suspect happened to mine and caused the low speed 20 amp fuse to blow.

My conjecture is that the fan is fine on these cars but the wiring, particularly on the low speed side, is the weak point.