I can't get my head around the attitude some people have toward the show in terms of 'replacing this or that' because I've seen it all already. So what? If you don't want to see it again don't buy the HD set. I've seen all the episodes too, but I've never seen them like this and it felt like seeing the show for the first time all over again.
The original effects are beautiful, and they honestly didn't get a chance to truly shine over the last 25 years. Season 3 was the only set I ever bought of the DVD release, so I fired up Sins of the father today and immediately after watched the new HD version. It's like seeing a totally different show.
If someone decides to go and revise all of the effects after all these sets have been released, then so be it, but I want to see the show as it was filmed and in it's original form. No TOSR revisionism thank you. The show is what it is.
If I want to see new effects, I'll find a new show to watch.