While it is an interesting conversation, I am seeing that some posters are confusing two completely separate thoughts as being the same thing. That is to say, "does the creator of a modification have the right to ask for money", and "does the creator of a modification have any rights at all".
I'll illustrate with an analogy - a pancake recipe.
If I come up with a new pancake recipe, based on a very famous pancake recipe, it may well be true that I shouldn't ask for money for it, or refer to the original pancake recipe, or use it for commercial purposes, or perhaps even refer to it as a recipe for "pancakes". I think most of us agree on that point. We may disagree on the degree of how wrong any of those things are (ie. damages), but let's put that aside for the moment.
HOWEVER, just because I shouldn't be asking for money for it, and may not even be able to use the work "pancake" in public, it does not hold true that I should give away this recipe to anybody who asks, simply because they want it in their own collection of derivative recipes. That is a separate concept.
Perhaps I'm satisfied to enjoy it myself, or occasionally for special guests who visit my home.
After all, even distributing the recipe for free might be considered to be against the law... so why would somebody put themselves at risk, simply because of the request of a stranger ?
Please think about this, while you're thinking about the first part.