My guess is that your opinion that Afroyim v. Rusk was a wrong decision will have little if any impact on any decision the Court may make regarding BHO's NBC status.
if he decided to carry forward a foreign citizenship at or after age 18, his U.S. citizenship is revoked, as I understand the law and I do not find that effectively refuted.
That is not what the U.S. State Department says.
One can day similar things about Dredd Scott and Roe/Doe.
It is for the court to decide and Congress to reinstill their responsibility to legislate.