I can give you a small piece of evidence to the contrary, that at least one of the founding figures thought that having a mythologized early history was extremely important for the country.

I would like to introduce you to the far-too-unknown Charles Thomson of Philadelphia, who was enough of a firebrand in his own town to be called by John Adams "the Sam Adams of Philadelphia, the life and cause of liberty". He was not moderate, in other words. When it came time to set up the Continental Congress, Thomson was shut out by more conservative elements in Pennsylvania, and instead of being a delegate (and thus a name people might have remembered) Thomson served as the Secretary.

This did two things: it made Thomson the official record keeper of the political side of the war for independence, and it made him unable to vote. Thomson took what power he had and used it, and as official record keeper had control over what was put into the minutes each meeting. This led to some disagreements at times, like a cane fight with delegate James Searle, who claimed Thomson had misquoted him, on the floor of Congress in which both men were injured.

Most importantly, Charles Thomson stayed and stayed--through the first Continental Congress, through the second, and through the Confederation Congress. He was, along with Hancock, one of only two people to actually sign the Declaration of Independence on July 4th, making it official. He was the only person to be present for all three of these Congressional sessions, and the only person who had a continuous, on the ground view of what happened in all of the political planning phases. Thomson was the institutional memory of Congress until the day he finally took on his last official job: delivering news to George Washington at Mount Vernon that he was the first president, and turning over the Great Seal (that he had designed, mostly).

To get to the point of your question, after retirement to his farm (a farm without slaves! Thomson was a Quaker abolitionist), he wrote about it. He wrote, apparently, more than a thousand pages about it, a massive history of the political formation of the United States drawing upon his first-hand, intimate knowledge of everything that went on behind the closed doors of Congress, including the quarrels and brawls.

Then he burned the whole thing. His reasoning: "Let the world admire the supposed wisdom and valor of our great men. Perhaps they may adopt the qualities that have been ascribed to them, and thus good may be done. I shall not undeceive future generations.”

So I'm not sure about whether the Washingtons and Jeffersons of the world specifically said this about themselves, but Thomson sure thought they (well, someone--we don't know exactly who) needed some buffing in order to be good role models. Fun fact: I visited Harriton House (now a small museum) many years ago, where I heard this story for the first time; it is probably the story that got me into history--it's such a great example of how tantalizing a subject it can be, and how many mysteries remain when it comes to the past.