It is my opinion, that the only reason to have Senators is to ensure that the procedures of constitutional rules and wisdom are followed by each state and that for each state, each county, etc. to act as wardens of the Constitution, so to speak, keeping three branches of government, etc. They could also act as guides to ensure that the Constitutional Rights aren't trampled upon within Legislative lawmaking -- having a voice, but without a vote. If you wanted, you could see them as the proofreaders of the law (perfecting the wording to be accessible to the people and that rights aren't being neglected), rather than lawmakers themselves.
The Constitution writes it opposite of what I say: that Senators should come from below to serve upwards, but that's what representatives already do. There is no other reason to ensure Senators. Having two bodies of legislators is confusing at best and debilitating and inefficient at worse.
You can already see the failure within cities and counties of the US: some counties make a committee of the elected official (commissioner), and some cities do not have a Judge at all, so that citizens issued tickets by city police must have a car to fight a case at the county court.
The Constitution leaves it ambiguous, but cities should have one appointed Judge, while county courts should have a single courtroom with two Judges, four for the state, doubling upwards to the national court, which should, but this reasoning, have eight Justices.