General Discussion

The point of the Senate is that it's a more deliberative body, representing larger numbers of people, which serves to moderate the power of the House. Mind you, Congress as a whole was more powerful when the nation was founded; they've handed off power to the executive over the years, for better or worse (really, a bit of both). The House was also intended to grow with the population, and if we'd followed the general guidelines for growth the Founders suggested, we'd have a House with more than 600 members. The number of seats was capped ~90 years ago, because Congress didn't want to fund another renovation of the capitol building to fit more people. Also keep in mind that the States had a more uniform population distribution when the country was founded. You didn't have California and Nebraska sitting with orders of magnitude of difference between them, so the difference in representation in the Senate was not nearly as significant as it is today.

Wether we need a secondary deliberative body in the legislature or not is a matter of debate and opinion. I can see why you'd want one, but I can also understand why people would think it's not useful anymore.