Even strictly speaking in regards to roadways the problem wasn't cancelling Spadina, the problem was not having any additional capacity north-south through the city wider than two lanes each direction between the 427 and the DVP. Ditto for crosstown after they turned St. Clair into the streetcar ROW.
Combine that with incredible growth and lack of transit building and you have the commuting nightmare we see today.
Six-lane roads and expressways are City killers and awful to live near.
They deliver pollution, congestion, physical and psychological separation between communities and deliver little back in return.
There is an argument to be made for additional 'arterial roads' in some portions of the City (very hard to do now); but might have been quite useful.
There remains a need to make it easier for pedestrians, cyclists, transit and cars/trucks to get over/under major barriers in this City, particularly highways, and rail corridors.
A lot of congestion is related to the need to get around said barriers.
But I, for one, am entirely grateful we didn't see any more six-lane roads than we did, or expressways, and frankly, I wish several we got hadn't happened.
I believe in the utility of highways for moving people and goods, between Cities/Regions, but not within them.
An excellent piece on these barriers, focusing on pedestrians, but usuable in many respects for drivers too.......is found at Metroscapes by Trevor Heywood: