Worked at Expo '67 in Montreal; one of the better World's Fair, at least in my opinion. In spite of higher than expected attendance at Expo '67 it was a loss financially for the city of Montreal. That has been the experience of any city hosting a World's Fair. Aside from the prestige aspect, which has diminished greatly over the years, hosting the World's Fair isn't worth the trouble and expense. Fewer cities are interested; countries and corporate entities willing to sponsor a pavilion at a World's Fair have declined ... which means they are now much smaller.
My family went to both the New York World's Fair and Expo '67. I was in fifth and seventh grades, respectively and both were wonderful experiences! It was during this time that my love for science was developing and how those two venues fed my imagination! (I also liked Rene Simard's rendition of "Welcome to Montreal" when the Olympics were hosted there.)