You're seeing this all wrong. No one said that the Constitution is perfect and should remain unchanged. The only thing that has been said is that the federal government should be forced to operate within the terms of the Constitution. If new situations mean that the Constitution must be changed, then great. Some of the best parts of the Constitution are the changes that were made since it was written.
And you're wrong about the level of interaction between citizens in the early US states. They were tightly linked in terms of trade, culture and defense. In a crude 5th grade summary: tobacco and cotton came from the south, machined tools and clothing came from the north. Grain, lumber, gunpowder, lead, iron, coal, cattle, etc. were all shipped between states in a web of supply and demand.
Furthermore, news was not rare. The early US had several successful newspapers that were widely distributed.
Anyway the question of the best balance between state and federal power doesn't matter until we the people have some way to effect it. Our current way, the drafting and protection of laws and documents like the Constitution, don't mean shit if the federal government can do as they please without regard for the rules. That most important first step is to demand that everyone play by the rules as they are written. The second step is to debate what rules we should make or repeal.