17th - The concerns that drove the struggle to free the Senate from the control of corrupt state legislatures pale in comparison to what we have today, with huge sums of money being openly given to Senate candidates (mostly incumbents) by lobbyists and activists. In this regard, the 17th Amendment is an abject failure. It can hardly be the case that the amendment strengthened the resistance of the Senate against the advances of special interests. Additionally, state legislators are (in theory) more beholden to the voice of their constituents than are Senators picked by direct election.
26th - Lifespans, educational years, and time spent dependent on parents' money have increased, and probably will continue to. Consequently, it makes little sense to allow 18 year olds to vote their immature and inexperienced consciences into law.
I can get behind this.