In this case, and speaking specifically around the time that the Constitution was ratified, I suspect a Congress that failed to exercise that power would have been replaced by a Congress willing to, since people liked receiving correspondence and it was fairly vital to doing any kind of long distance business.

Lol, a government will always exercise any power it is given, and that's why your laws must be overly limited in the first place.

Just see the interstate commerce clause and what's happened with that