I, for one, prefer to keep government as close to the States as possible.
That's precisely what it was in the era prior to this Amendment. This notion that somehow the Senate membership would improve dramatically with its repeal is pure pie-in-the-sky fantasy. I wouldn't WANT my state legislators choosing my Senators. It's bad enough I'm disenfranchised with respect to my legislative members and my Congressional district (one party for 136 years, not GOP), but take my vote away for U.S. Senate, and my disenfranchisement will be complete for both Congress and the state legislature.
For what it is worth, that very phrase, the Senate as a "millionaires club", originated in the 1890s, well before the direct election of senators.
Indeed, at the Senate's own website, you have this recounting of the Senate under Vice President Morton (1889-1893):
The Businessman's Cabinet and the Millionaires' Club Just as Harrison's cabinet was called the "businessman's cabinet" for its inclusion of Wanamaker and the Vermont marble baron Redfield Proctor, the Senate over which Vice President Morton presided was dubbed a "millionaires' club." In the late nineteenth century, businessmen had steadily gained control over both the Republican and Democratic parties and used their political positions to advance their economic interests. Senators became identified as spokesmen for railroads, timber, mining, and other industries. As California Senator George Hearst, who had made his millions in mining, proclaimed: "the members of the Senate are the survivors of the fittest." It seemed appropriate, therefore, that the Senate's presiding officer should be one of the nation's most prominent bankers.
(Trivia note: not only was Vice President Morton one of the nation's most prominent bankers, but the infamous community of Morton Grove was named in honor of Vice President Morton, albeit that naming was many years before he served as vice president.)