That is the correct behaviour. The Address in System Preferences shows you the Hardware Mac Address. This is the default address and can not be changed without physically replacing the wireless card in your Mac. Your MAC address will always reset to this on a computer restart.
WifiSpoof changes the software MAC address. This is what your computer broadcasts to other devices.
@pamala Are you sure this is WiFiSpoof, as it doesn't touch any network settings apart form changing your Mac address. And the only way this would affect your speed, is if your router is configured to limit speeds to the new Mac Address you are using.
Well, I must say that I am not 100% sure if it actually worked with the Wifi. It did change the MAC-address for the network card en0, which I recently realized is the ethernet card. And I did have the ethernet cable connected earlier. Only later I realized I was not observing it changing the en1 (Wifi) MAC so I don't actually know if it worked with the Wifi or not at any time.
So, IMO it can be one of the following:
WifiSpoof never worked with late 2009 (or late 2010) iMac Wifi card
it did but Wifispoof update caused it to stop working
or updating Mac OS Sierra to High Sierra + possibly one or both things above = not compatible