I don't think there's a need to worry about proximity affecting price either. At least not until more rush hour and hourly RER service comes (whenever that will be), since the supply of GO service is still limited to a few trains in and out book-ending the business day and the express buses. The downtown residential market overall would be the prime factor in pricing, for now.
Even when better GO train service arrives, I doubt there will be that much of a spike close to the station vs. sites several blocks away -- all are a relatively short walk.
And let's remember that "transit oriented development" is supposed to be a good thing.
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