It is thought CN went to the small state side because it feared the new western states would rapidly increase their population and come to dominate the House of Reps. It was also clear that despite the problems with a State based confederacy, the States were an elemental part of our traditions and had to be represented. It is doubtful the people's delegates would have ratified the Constitution without this provision.
Despite the close vote, the feeling was that it would not have been if NY, NH and RI were present.
From the Framer's viewpoint, the 17th amendment was a double disaster. First,they never seriously considered popularly elected officials for more than two years. The only reason we do not have annual elections for reps is that travel was so difficult in the 18th century.
Second, a democratic based Congress would be sure to eventually trample upon the rights of property, contracts, sound money. One house was to protect the people, while the Senate would protect the men of property.
I doubt that the 17th could be repealed, but I have wondered if the states could amend their constitutions to allow for right of recall on vote of 2/3 of the State government or something, providing that the voters in each state approved it. Course recall can open a can of worms too.