I offer Paine's words as a contemporary of the framing of the Constitution. He wrote his comparison of the Presidency at a time when it was fresh in people's minds. I have not seen other writings (other than Jay's letter to Washington) on the intent of the natural-born clause.
I agree that Paine became a bitter man later in life. He was ostracized from society, and died alone with little acknowledgement.
I read a letter of Paine's from 1807 that is on display at the Thomas Paine House in New Rochelle, NY. In this letter, Paine pleads with Vice-President George Clinton to testify on his behalf to a local election board that refused to allow Paine to vote, claiming that he was not a citizen.
Paine wrote: "As it is a new generation that has risen up since the declaration of independence, they know nothing of what political state of the country was at the time the pamphlet Common Sense appeared; and besides this there are but few of the old standards left, and none that I know of in this city."
Clearly, he was a forgotten man in his old age, largely due to his own later behaviors. Still, that doesn't take away the value of his earlier contributions.
-PJ
Tom Paine was a real character, a genuine radical. I don’t think anyone ever accused him of being too conservative for his time.