To start out with, I thought we would all like a review of the Seventeenth Amendment to the United States Constitution:
The Seventeenth Amendment of the United States Constitution amends Article 1 Section 3 of the Constitution to provide for the direct election of Senators by the people of a state rather than their election or appointment by a state legislature. It states:
The Senate of the United States shall be composed of two Senators from each State, elected by the people thereof, for six years; and each Senator shall have one vote. The electors in each State shall have the qualifications requisite for electors of the most numerous branch of the State legislatures.
When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies: Provided, That the legislature of any State may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.
This amendment shall not be so construed as to affect the election or term of any Senator chosen before it becomes valid as part of the Constitution.
I have always been a big supporter of State powers over Federal powers. I have also said over and over, if there is ever going to be a rebellion against a corrupt Federal Government/President, it will come from the States and not individuals (like the Civil War: even through the States rebelling were wrong, it corrected the injustice of slavery). To this end, I think there is a gross inbalance power between state and federal government. I have name this inbalance The Seventeenth Amendment.
I'm sorry to put this to you people, but we are not a pure democracy or, at the very least, the Framers thought we should be a confederated republic. A shared power between State and Federal government, and if you look closely at the original wording of the Constitution, the only people directly elected to the Federal Government was the House of Representatives. Why was this done? To deny special interests:
"In republican government, the legislative authority, necessarily predominate. The remedy for this inconveniency is, to divide the legislature into different branches; and to render them by different modes of election, and different principles of action, as little connected with each other, as the nature of their common functions and their common dependencies on the society, will admit." ~James Madison, Federalist No 51
Unsurprisingly, the Revolutionaries were not very impressed with most aspects of the British model of government. They rejected parliamentary government, with its king or queen and three estates of the realm (lords spiritual, lords temporal, and the commons).
But one feature of the British system, the Framers did borrow. That was bicameralism - a word coined by Brit Jeremy Bentham to describe the division of the legislature into two chambers (or, in Latin, camera).
The British Parliament had its House of Lords as the upper chamber and the House of Commons as the lower chamber. Citizens selected members of the House of Commons. The members of the House of Lords, in contrast, were those who had been titled by a king or queen (lords temporal) and the archbishops and bishops of the Church of England (lords spiritual).
Loosely basing our bicameral legislature on this model (minus the lords, both temporal and spiritual), the Framers created the House of Representatives as the lower chamber, whose members would be selected directly by the people. And with almost unanimous agreement, they determined that members of the upper chamber, the Senate, would be selected by not directly, but by the legislatures of the states. Each state would have two Senators, while Representatives would be apportioned based on population.
Repeal of the amendment would restore both federalism and bicameralism. It would also have a dramatic and positive effect on campaign spending. Senate races are currently among the most expensive. But if state legislatures were the focus of campaigns, more candidates might get more access with less money - decidedly a good thing.
Returning selection of Senators to state legislatures might be a cause that could attract both modern progressive and conservatives. For conservatives, obviously, it would be a return to the system envisioned by the Framers. For progressives - who now must appreciate that direct elections have only enhanced the ability of special interests to influence the process - returning to the diffusion of power inherent in federalism and bicameralism may seem an attractive alternative, or complement, to campaign finance reform. 
Today, state governments are nothing more than glorified lobbying groups trying to get any scraps of power and money from the federal government. Sure we should have a strong central government, but power should come from the bottom up and not the other way around. Senators are
elected, sorry, chosen with a popularity contest every six years at a time and not accountable to anyone. The Average Joe doesn’t know what their Senators are doing in those six years. I bet you anything that a person will be elected to the US Senate no more than three times if the 17th is repealed.
You ever watch C-SPAN and see some poor sap get grilled by US Senators? What is good for the goose, is good for the gander. I would love to see them grilled for their actives and laws that they voted for/against. State legislatures are more equipped to hold them more accountable than we will ever have (think about the $700 Billion Crap Sandwich). State elections will also become more important than they are today.
Zell Miller (D) once said that the 17th Amendment has "allowed Washington's special interests to call the shots, whether it is filling judicial vacancies, passing laws, or issuing regulations." If we are really serious about reforming government, let us start with the US Senate. Nowadays, more lobbyist money is spent on the US Senate than any body of government. It is way too easy to focus on corrupting just 100 people. You would need billions to corrupt 50 full state legislatures. Senators also will not need those millions just to get elected/re-elected.
So in closing, repealing the 17th Amendment would do three things for us: (1) give more accountability to the US Senate, (2) give more power to the states, and (3) reform campaign finance.
PS: Please check out The Campaign To Restore Federalism, a nonpartisan effort to repeal the Seventeenth Amendment.