Or with the federal income tax -- the 16th, rather than the 17th amendment. Combine that with the world wars that required and (in most people's minds) justifiec higher federal taxes, and you see a reversal of the situation under the Articles of Confederation.
Right after the Revolution, the federal government had to beg for money from the states. With the Constitution it got its own limited right of direct taxation. With the federal income tax, Washington DC eventually became the great source of funds for state projects. Combine the tax with the federal governments greater ability to borrow funds and incur debt and its control of the monetary system and it amounted to a major shift in the relation of the federal and state government.
The founders obviously didn't intend that, but I think maybe they were of two minds. They were creating a federal government that would draw the states closer together into a national union. They built a capital that would act as a magnet for politically ambitious people, drawing them away from state and local politics.
But they still thought of the states as in some way distinct cultures: Massachusetts and Virginia, New York and Maryland, Pennsylvania and South Carolina. As the country grew closer together, as new states were added that didn't have long traditions, as political talent concentrated in Washington, it was going to become harder and harder to maintain the older model.
Good post.