I personally found that parts of downtown & the surrounding areas are somewhat similar to parts of Queens & Brooklyn, but obviously many parts of Queens are Brooklyn are low-rise, like most of Toronto is.
I'd like to see more mid-rise happening like DUKE, B-Street condos, and the Hive condos throughout the city, since you mentioned mid-rise.
In terms of vibrancy, one key element is narrow store-fronts, it's not necessarily about the height. Other things that matter are how narrow the street is, if there are trees, sidewalk width.
Personally I love places like this in Toronto:
http://goo.gl/maps/KP2b5
Many condos get this wrong because they have wide-storefronts and tend to attract things like banks & big chain restaurants. However, most of the condos built were built on parking lots or former rail/industrial lands, so they added vibrancy & density to the city, there is no loss.