New to Wagner - Just purchased this big box set.

[Jo498]

It's explicit said that Siegfried is supposed to be the free hero, "freier als ich, der Gott" (and also more free than Siegmund). That he falls prey to the intrigue and thus fails in a sense (or maybe the sacrifice is part of his purpose) is another story.
Obviously, several different mythical tropes and archetypes are mixed together. (E.g. in the later medieval, somewhat christianized version there is no kinship between Siegfried and Brünnhilde, she's just that indomitable warrior princess from afar.)
Incest is not necessarily negative in myths even though to my knowledge European/Norse/Indoeuropean traditions didn't have royal sibling marriages like the Egyptians or Inca.

[Karl Henning]

However symbolic you may wish to be, I see no reason to discount the literal interpretation. I doubt most operagoers would see the Siegmund-Sieglinde union as only symbolic: "Oh, so brother and sister had a baby together? That's incest!" "Yes, but it's symbolic incest." "Oh, then it's all right." And of course we can be sure that Siegfried and Brünnhilde got it on after the curtain falls down following the close of his eponymous opera, and since she's his grandfather's daughter that would make her his aunt, pretty incestuous too though no one mentions that inconvenient fact.

As for your statement that "Their child Siegfried embodies the liberated hero, born to renew a corrupted and decaying world, which to my mind is the central motif of the entire cycle," I would certainly agree that "renewing a corrupted and decaying world is the central motif," but is Siegfried really the "liberated hero"? Certainly Siggy has no ambition to wield the power conferred on him by the ring, but he still falls prey to the ring's curse by committing two murders in Act Two of Siegfried, and after drinking Hagen's potion, he spends much of Götterdämmerung not as a hero but as Hagen's pawn.

It's really not Siegfried but the former Valkyrie and now fully human Brünnhilde who redeems the world at the close of the cycle, sacrificing herself and restoring the ring to the Rhinemaidens while Walhall goes up in flames and Hagen is drowned in the Rhine.

And so regardless of any European mythological thought, I don't think the facts of Wagner's story bear out your theories.

Anticipating that Siegfried snuffs it is my current Schadenfreude. 

[Mapman]

It's long enough since I did any reading about Der Ring, that I'd clean forgot Gunther, Hagen and Gutrune, so the freshness of this episode is an added bonus.

I'm not sure if you've gotten that far yet, but the transition to morning after the night-time scene with Hagen and Alberich contains one of my favorite uses of bass clarinet.

(When I first heard the Ring, I was fascinated by a website that explained the musical relationships within various groups of Leitmotifs. I've unfortunately not been able to find that particular site since then.)