When the country was founded the entire population of the country was less than the current population of Chicago, and there were only a handful of cities with more than 5,000 people, which today is the size of a large high school.
Not to mention the astronomical differences in technology and interconnectedness, both between ourselves and other nations. There are plenty of places in the government to trim off some fat, but getting rid of things because they aren't in the Constitution is silly. Doing so completely ignores the will and purpose of the people that created those additions in the first place.
Our Constitution is pretty spartan. It is a framework, a foundation, not the beginning and end of everything. It was specifically intended to have some flexibility to adjust to changing conditions, and it has. Even were there a discrepancy between it and the current government, the solution is to change the Constitution, not scrap the government.