How important? Depends how you make your living. I've heard of an Assistant Professor of history in the US who got into near-sacking trouble because, when discussing Lincoln in class, he corrected a student. The student said that Lincoln was a slave-owner: the Prof said no, perhaps he meant Washington or Jefferson; then the whole thing ran out of control. Beware.
I am sometimes amused by claims like this.
Lincoln a homosexual? And no one alive during his lifetime ever recorded even a hint of suspicion on paper?
Remember, Lincoln was derided with a large number of epithets during his run for office, and his Presidency.
As far as the Jefferson case goes: How did they divine that since Jefferson was not Thomas Woodson's father, Sally Hemings could not have been his mother?
And I like your take on it: what is so important about the sex lives of these past Presidents?