Eugene suggests that the existence of state constitutional rights is relevant to whether there is an analogous federal constitutional right because it sheds light on “whether the right is firmly rooted in American law.” But I’m not sure how firmly rooting a right in state constitutions sheds light on whether the U.S. Constitution protects it.
As a general rule, states are free to draft pretty much whatever constitutions they want (republican form of government questions aside). So a state can establish a constitutional right not to have one’s labor treated as a commodity, see New York Constituion, Art. I, Sec. 17 (“Labor of human beings is not a commodity nor an article of commerce and shall never be so considered or construed.”). Or it can establish a constitutional right to have English as the official language, see Arizona Constitution, Art. 28. Or it can establish a constitutional right to have contributory negligence treated as a question of fact for the jury, see Oklahoma Constitution, Section XXIII-6.
State constitutions are chock full of such things. But as far as I know, these state constitutional rights don’t generally change the meaning of the U.S. Constitution. Constitutional rights don’t generally seep from one sovereign to another.
Granted, state constitutional law can become relevant to federal constitutional law in some contexts. Take the Eighth Amendment (please!). Under the Supreme Court’s current head-counting approach to the Eighth Amendment, state constitutional law could in fact influence whether a particular punishment amounts to “cruel and unusual punishment.” But I don’t see the relevance of that head-counting approach in the Second/Ninth/Fourteenth Amendments-and-Associated-Penumbras context that we are considering here.