You answered your own question I think. SCOTUS under Taney held slaves were not citizens, so that was the law of the land. I believe it was the 13th rather than the 14th amendment which granted citizenship. So the Taney era had a short half life.
Pre-Dred Scott there were places in the North and even the South where free blacks had many of the same rights as free whites, but there were also places that barred free blacks from voting and other such marks of citizenship. It's so ridiculously lacking in consistency. I guess that's what Taney was trying to do by coming down on the side that even if Dred Scott were no longer a slave (and he was still a slave) he was inherently a noncitizen.
Yes, Taney "clarified" the law, and per his ruling, it was unconstitutional for blacks to be voting anywhere, assuming one needed to be a citizen to vote (I guess not for state offices, but certainly for federal ones, you need to be a citizen).
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