While Mr. Calatrava’s Spire was condominium only, the mixed-use concept presented by Gensler not only opens the space up for the enjoyment of more people, it can also be far more financially lucrative. This trend is already seen in New York’s Empire State Building which today brings in more revenue from its observatory than all of its commercial tenants combined. Chicago’s AON Center, the city’s third tallest building, is also reportedly considering the addition of an observatory for this very reason.