Yes, converting the old low-rise buildings to new mid-rise buildings in Toronto is an effective long-term solution.  For those who are curious about this solution, drive/walk along the Bloor Street (along the Bloor subway line) or Yonge Street (along the Yonge subway line), you will see so many low-rise, low-density, and low-quality old buildings.  It is time to re-develop those areas.