It didn't bother me too much that the first two parts of the show ended predictably, since the predictability didn't detract from the comedic effect. For example, in the first section, it was not surprising that the last Homer remaining turned out to be a clone (despite that the original acted differently than the clones), but the fact that Marge didn't mind was an excellent addition. Over the summer I had forgotten what a variety of different levels of humor The Simpsons had started using (mirroring the style of Futurama, in my opinion)...no wonder it appeals to everyone. How is it that so much imaginative, witty creativity can come together without some cataclysmic result? Or maybe The Simpsons is that result....
It appears I am getting over my nitpicking of plot holes, since the time-travel impossibilities of this episode barely occured to me at all. I guess it's just because the so-called errors aren't quite important in this obviously fictional story.