@Grishka: Thanks! Yeah, a lot of people have told me that and say that, (but I need to keep it in mind) that the aim in doing a retelling is to find the core, or the bottom line as you call it, of the original and work that in.

•(Rambling thoughts)*

For example, I see this one as having three cores, and none of the is about killing a dragon. One is about the negative effects of greed; Andvari's hoard affects everyone that comes into contact with it, and leads (indirectly) to their deaths. There's a reason why everyone either dies or is psychologically broken at the end. The other is about the meaning of honouring your obligations and dishonouring yourself (related to the first one, and it's more of "how greed can lead to corrupted morality/dishonour") Brynhild has been forced to break her oath to marry the man who rode through the fire, dishonouring herself. Sigurd is also dishonouring his obligation and himself by tricking her into marrying Gunnar, but also honouring his and Gunnar's oath., so honouring your obligation may also lead to dishonour. Avenging your relatives as in "sins of the fathers" is also related to this. The "core" is essentially something that makes the story

The other one is the idea that the fate of a large number of people is inexorable and hard to change- that some actions are regulated by fate, and because you can't fight fate, you shouldn't try to change it.

As to shorter tales; IMO, say, the Grimms' early version of Rapunzel has the core of "overprotection of children, especially girls, is bad, because they'll eventually have to deal with the world on their own, and be unequipped to deal with it. Children need to mature away from their parents." Cinderella is essentially about stepparents and stepchildren competing for attention/resources with biological relatives. The core is essentially the part of the story that defines it, that makes it universal.