I went for the Bicentennial (yes, 40 years ago). BOY has it changed!!
First - paved parking lots. Then, past the Mount Vernon Inn and shops, there's a huge theater & education complex. All the outbuildings are restored & have living history actors.
All the fields have livestock (I forgot to get a photo of the sheep, darnit).
All the gardens have stuff. And there are a LOT of gardens. The botanical garden, the experimental garden (George was quite scientific about finding crops that would thrive on his land). The fruit and veg gardens. And those are the ones near the main house!
There's a trail through the forest with educational stops. Hear the bird calls George never heard! See the tracks of the local wildlife in his day! Guess the name of his dog!
Down by the river, The seawall was raised, so the marshy bits near the water are more living history and crops examples. There was a boatwright actually making a boat with period methods. The tobacco barn - they'd actually grown a saleable amount of tobacco (probably can't sell it; modern strains have way more nicotine). There were all the different types of fences, how they were made, and what they were used for.
There's even a pier and a boat tour now!!
7.37 miles walked, which is still a lot for me. Really interesting stuff!!