Roman law had a significant influence over the modern-day laws of many countries. Legal ideas like trial by jury, civil rights, contracts, personal property, legal wills, and corporations all were influenced by Roman law and the Roman way of looking at things.
I believe that the direct effect of the passage of the Seventeenth Amendment is that it improved representation of the people, because now they were able to directly choose Senators, which made the whole voting process a lot democratic.