Your post was well written. But consider this: obviously the Framers would, as you have stated, be unhappy with either extreme federalism or extreme decentralism (Articles of Confederation). But there is a great deal in between these extremes. Toward which extreme do you think the Founders would be biased?
IMO, the Founders wanted to give the federal government just enough teeth for it to be able to accomplish the tasks listed in the Constitution...and no more. They had seen the effects of an out-of-control government and fought and bled to be free of it. Yes, they would've been sceptical about state right's absolutism, but they would've been much more appreciative of the state's holding very strong footing vis-a-vis the federal government.
So long as the states did not attempt to infringe on the federal authority granted by the Constitution, I think, as the Tenth Amendment indicates, that the Founders would've been satisified with such a federal-state arrangement.
Tuor
But the Founders not only had experience with the oppressive centralization of the British crown. They'd also had to cope with the very inefficient and chaotic decentralization of the Articles of Confederation. While a Sam Adams or Patrick Henry clung to the state above all else, Washington, Hamilton, Adams, Madison and others did work to create a more effective national government.
And given a less centralized political order than we have today, I still can't imagine George Washington agreeing that a state had a right to pick and choose which laws it would obey and which it would violate. I suspect that for Washington, the question didn't even come up, the assumption being that federal and state governments had their legitimate spheres of activity and the expectation being that each would stick to its own sphere, with the states granting the federal government its right to legislate on those matters outlined in the Constitution. In 1787, they apparently didn't forsee the kinds of conflicts that would develop.
We can talk about what the founders might have said had they come back at various points in our history. The technological and social change would have made their heads spin. Were they to come back today, they would be shocked and appalled by the growth of government and the decline of liberties. Governments are involved in matters that no one would have expected them ever to have a hand in. And the rise of democracy would also appall them. But I'm not so sure that Washington or Adams or Hamilton or the later Madison would make so many objections to the decline of the absolute idea of "state sovereignty." The fact that the country had been able to survive and overcome the jealousies of the various states might well seem to them to be a great achievement, though learning about the Civil War would be a bitter blow to them.
Similarly, I'm not at all convinced that had they seen 1860 the Founders would have cheered on the Confederates. Those who would tear up all their work so shortsightedly would appall Washington and Hamilton. Jefferson, the vain intellectual, would probably have been flattered by the Confederates' references to himself, but the mature founders who had seen how hard it was to establish our federal system would not have condoned breaking it for such trivial reasons. And I'm not so sure that the Founders would have believed that their work had been destroyed had they returned for the centennials of the Declaration and the Constitution. Deploring the Civil War and the intrusion of force into our politics, they would have seen the nation face its second century stronger, more confident and with the federal system and limits on centralized power intact.
But what if the Founders had returned to Virginia or Alabama circa 1950? They would see democracy in check and states asserting their independence against the federal government. But what would they have thought about segregation? Rockwellites dismiss segregation and slavery as things that would "naturally" have been overcome, ignoring all the appeal of these institutions to some and all the struggle required to get rid of them. Jaffa may be wrong about some things, but he does take these questions seriously, and is trying to mediate between the Founders' worldview and our own moral universe. If there is no continuity between the two, if they accepted what we can only reject, then a rift is opened up in our history that can be very destructive of our institutions.
It does seem that having created checks on the federal government and securing basic liberties against it, amendment of the constitution to protect those rights against encroachment by the states was not wholly out of place. The Bill of Rights itself was such a revision of or addition to the original scheme, and the inclusion of an amendment process in the Constitution itself implies that such revisions would be necessary over time.