I agree with your view of OFAH in it's original run, I'm just not bothered about them making a few extra episodes later on.
My original response was a more general point than just getting at you, some people go on as though they made another 20 episodes or so and ruined the whole thing.
I've never been bothered by the idea that programmes, bands, artists etc. 'ruin their legacy" or however you want to phrase it by going on too long. I grew up watching the Simpsons when it was good and that's about 25 years and 400 episodes ago now. But that doesn't alter my view that the good...
The way people go on about this you'd think it'd gone on for about 5 series after that "final" episode. There were only 3 more christmas specials between 2001 and 2003.