I dont think the 17th amendment had the effect of lessening corruption as its designers intended, but getting rid of it wouldn't improve things much either. Restricting campaign donations to only in state residents might bring closer to original intent.
As I posted elsewhere Ireland almost did do away with its Senate, and likely would have if the unpopular Prime minister asking for it wasn't also asking for other powers. I think it would have saved a substantial amount of money to do so.
A National Initiative option such as Switzerland has, would also be beneficial, tho I wouldnt trust computer technology for voting.
One of the the original proposed bill of rights amendments, tho poorly worded, intended to guarantee at least one representative for every 30,000 residents. While it probably wouldnt be practical to raise it that much, we could increase the number of representatives.