Anna:
My hat off to you! What an incredible group of photos. They really represent a time long past, the kind of thinking that would lead to the Spadina Expressway. It was the same post-war thinking that laid waste to the chestnut trees of University Avenue, and widened Avenue Road into a mini-highway (at least until it hit Forest Hill).
In typical Toronto fashion, the extension of Mount Pleasant through Rosedale was more of a "muddling"-along approach in improving traffic, that followed the path of least resistance, through ravines (similar to Rosedale Valley Road) and a neighbourhood without (at that point) a lot of political clout.
If we connect the dots, we can also see a relationship between this suburban commuter link and the ultimate proliferation of parking lots in the east downtown resulting in the destruction of the historic "Old Town".