If they could achieve that high of a literacy rate with those adverse conditions they had, it speaks very highly of them. If the Declartion of Independence is any example of the general intelligence level of the people of that time, then yes, let's get back to it. Not to mention any other historical documents, speeches, and literature produced in that era. That kind of quality is sorely lacking today.
How much do you want to bet that I can prove that the literacy rate of the population was nowhere near 90%?
"If the Declaration of Independence is any example of the general intelligence level of the people of that time, then yes, let's get back to it."
I can find just as many intelligent people today as the number of people involved in writing the Declaration, does that make s just as intelligent?.