I understand the principle you are talking about but in essence you are comparing apples and oranges in terms of how a law affects people.
The public domain issues your talking about occur basically because the author is long since dead and heirs are not identified or have made claim to the property in question. If an author has been dead over a hundred years their work is in the public domain just because it's no longer reasonable or possible to identify receivers of copyright payments. Once a spouse or immediate family have passed on, and a hundred years pass, it seems a little silly to try and make payments on property when the author can't even enjoy or receive payment. Dan Curtis had children and other reps with long standing vested interest in the DS property.
Screenwriters and others who adapt stories long since in the public domain usually acknowledge the source by saying their new work is based on a story by so and so, etc. They aren't doing anything wrong or immoral. They aren't alone in building upon an existing story, adding and twisting around things to create a new work/new idea. Existing ideas provide plenty of fuel for the fertile imagination, to seize upon the first idea and add another idea to that, and this is true in any business in the world not just the entertainment business.
I do also have to say that the legal issues you pointed out are horrible wrongs perpetrated on fellow human beings, devastating crimes against humanity. In this particular topic, we are talking about a freaking movie. That's all it is - a movie. If it's an awful movie, fandom will continue. If it's a great movie, fandom will continue. Lives will not be ruined in either case.
If indeed the DS fandom ended tomorrow and there was no where to discuss it and no way to by anything related to DS, the world would go on and I think most of us would manage to live the rest of our lives rather happily. I believe the focus should be on what fans CAN do creatively to celebrate DS and not what they can't do. Fanzines like the one Taeylor is starting is a good example. He will undoubtedly be using DS photos and short stories based on existing characters but won't be bothered by DCP. That kind of project is rarely ever bothered by those legal folks. The people who make DS products available to fans have every right to decide what they want to see done with their property. To bitch and moan about what they want to do with their own property is rather unseemly. People who do that really don't have any right to complain, IMO.
I guess this is going off topic somewhat so I'll rest my case now, lol.
Again, just because it's the law doesn't make it right.