GO is an enabler that allows people to buy homes in the outer suburbs. Essentially GO allows an individual to live further away from downtown, have a larger house and property, but maintain the same or a shorter commute time from downtown than living in the 416.
GO ensures that you can live 30 mins from the nearest GO station on a 1 acre lot that you bought for half a million in Clarington, and still make it to Union in roughly the same time that it takes a rider in Scarborough using the TTC to get downtown.
It's true that if GO was not there, we would have lots more traffic on the 401 and the Gardiner. Paradoxically, that would probably have resulted in higher parking rates downtown (with higher demand), and increased commute times, deterring many from moving further away from the 416.
What I was saying was that people don't make the choice to move to Clarington because of the GO service. People move to Clarington because they can buy, using your example, a 1 acre lot for half a million. While a GO Station may be somewhere on their list, I would still say it's not a "clincher".
The future of GO stations will be really interesting, as I said, with the mobility hub concept being initiated. I'd also like to see GO experiment with paid parking, perhaps as a pilot program on one line first. Even if you charge a dollar a day, people will be forced to think twice about taking their car to the station.
It is true that in the far suburban stations, such as Milton, there is fairly thin transit service to the station. However, in the inner suburbs such as Scarborough, for many there is no excuse but laziness to make such a decision. (Keep in mind there are other options, such as taking your bike or walking. I have a 20 minute walk to the station every morning and I see people who would have a 10 minute walk driving past me). As long as parking fees are matched with improved transit connections, it will be a winning situation (and by improved connections, I mean both routes, as well as fare integration.)
As others have said before me, GO is not an enabler, it arrived only after the sprawl began. We had a choice-- increase road capacity, or move people in a more progressive matter. Ignoring the suburbs has never been a choice.
And KeithZ, there's one thing that's missing from this discussion-- the fares that people pay for GO service are much higher than an equivalent trip (if indeed there is one) on the TTC. It's an express service-- you pay for speed.