Folks, just to let everyone know, for the time being, I have abandoned using macOS Sierra on my early 2009 iMac, and I have returned to using the last build of El Capitan.
I won't take up all of your time with the details, but suffice it to say that I had a very nasty experience with the 10.12.1 update this morning which resulted in my keyboard, my Magic Mouse, and even my wired mouse becoming totally inoperable, so that I could not log into my active system.
I tried everything multiple times: resetting the SMC, zapping the PRAM, booting into Recovery Mode, and trying to boot into Safe Mode.
Ultimately, I had to install Mountain Lion on another external partition, and then from there reformat my internal hard drive, and do a clean install of El Capitan.
I have been at this all day working on getting everything back in order, and I am still not done yet, and I am tired.
This old iMac -- almost eight years old -- doesn't have too much time left on it, so I will be sticking with El Capitan until I can afford to purchase a new machine. Everything I have been through with Sierra on this machine just isn't worth the hassle for features which I really don't need, and which I even wouldn't use.
Thanks again to those of you who have worked so hard, and invested so much of your time, to help us get Sierra installed on our machines.
The question is, given the general age of our machines, and the problems and challenges we have had to endure, in order to get it working on our machines, is a Sierra upgrade really worth it? Looking at Apple's list of selling points for Sierra, I have come to the conclusion that at least in my case, the Sierra upgrade has not been worth it. Thus I have abandoned it, and I in fact have a peace about it.
Not only that, but because I performed a clean install of El Capitan, and also stopped using a number of apps and system enhancements, I have noticed a renewed snappiness in my machine, particularly in how fast apps load now. So again, I am pleased.