That problem isn't necessarily isolated to Sparks Street though, look at the rest of our CBD right now. With such a huge portion of it dedicated for public service (and most of them not working downtown anymore and very reluctant to go back even on a casual basis), many retail spots & downtown businesses are having trouble surviving. Without a good base of everyday customers (employees in the area & local residents), no amount of subsidies on rent will make businesses on Sparks St lively or thrive.
On the note about improvements, one thing I find missing downtown are wayfinding signs. How hard would it be to have a few of these installed to show where LRT/bus stations are, public washrooms, directions, etc... I like the new ones on Rideau Street