I was lucky enough to live close enough to the New York Fair that I lost track of the number of my visits. I was also fortunate to have the opportunity to stay with a family friend in Montreal and spend a week at expo67....and returned a year later for a day at the first season of Man and His World.
As others have said, both were magical places and had very different vibes. In retrospect, expo67 was more well-designed and New York's was garish, but the adventures to be had in and around their respective pavilions were glorious!
Thanks to this site and other online resources, we have an incredible amount of material at our fingertips... a far cry from the few ephemera I had kept and the occasional Fair retrospective exhibits I managed to attend at the Flushing Town Hall and the Queens Museum.
The flat park that tops the old Corona Dump is hallowed ground; I feel its electricity every time I step into the park.
I haven't revisited the expo site since 1968; judging from the pictures I've seen i'd feel very out-of-joint if I visited it today.