I feel like a good balance here would be putting a mixed use complex over the east block, since it can easily have commercial components on Spadina/Front and a quiet residential lobby on Blue Jays Way. Then, everything else can be made a park, with the possible exception of the space directly above the GO platforms. There's little point designating both sides of Spadina as a single park, it's a busy thoroughfare that most pedestrians won't want to cross.
The current proposal pisses me off. They don't seriously expect the city to fund and build the entire rail deck park, do they? Because "potential contribution" to me reads a lot like "get bent".