[officedweller]

The viaducts are fine - they are only a visual barrier, not a physical one.
i.e. it's not constructed of bents like the Gardiner in TO with an arterial directly underneath it. It's actually quite unobtrusive, compared to say, the area below the Burrard Bridge or below the Cambie Bridge.
The undeveloped nature of the land below the viaducts is a function of Concord Pacific making the northeast False Creek area the last phase of development. Remember that the are below the viaducts held railway tracks and warehouses until redevelopment for Expo 86 - so there weren't many buildings there to begin with.
Without the viaducts, Pender, Hastings and Water Streets would be constantly clogged.