No, none of this makes sense to me.
There are two subways that are "close" to Yonkers Raceway. The 2 train is almost two miles away, and the 1 train is four miles! Nobody is going to do this to get to a match. Even the railroad is a mile and half. Stamford is quicker because it's on Metro North, but that cost $25 round trip. Also, how are you going to fit 20,000 or 30,000 people or so on packed rush hour trains out of Grand Central? How many trains will they need to have going back into the city at night to get everyone back home? No, this is crazy. It was a mess getting everyone to Red Bull Arena and that was only a couple of thousand people. Now imagine 10x that many trying to get to Stamford. There's only four trains going back to the city between 9:56pm and 11:04pm. Can they fit 20,000 in? Also, people are willing to wait for a subway or two because they're only a few minutes apart, but who's going to want to wait for that fourth train at 11:04pm? That's two hours after the match ends.
It's not even worth starting a Mets/Yankees argument. You're talking about attendance *this* year, but season tickets lag a year or two behind team performance. If the Yankees place 4th for five years in a row how many season tickets will they sell in year 5? Or if the Mets win the Series this year yes, there'll be an increase in season tickets next year, sure. But it's going to take maybe five years in a row of good (and winning) teams to get a large increase in ticket sales. So sure, Jeter and Rivera sold a lot of season tickets to people who are still sitting in the stadium but they're both retired now. If the Yankees start losing for a few years in a row they'll still sell tickets but not nearly as many. And the Mets are the same, if they start their own "dynasty." It's going to take a number of years to get that up to speed though. To compare Mets vs. Yankees ticket sales has far too many variables. As another factor in ticket sales, people have been calling for Terry Collins' head as recently as the All Star game but now that they're winning he's a genius. (I may be saying the exact same thing about Kreis in a couple of years, but that's a different argument.)
Anyway, the point is that ticket sales have less to do with the fan base and corporate spending and far more to do with how the ownership is willing to build the team. If the Mets continued their non-spending ways we wouldn't be where we are now this season. But they shocked everyone and got a few good players and now they're in the playoffs. A few more years of this and who knows? But *that's* when we should be discussing season ticket sales and attendance numbers, not now after they've been awful for a number of years.
Anyway, my point here is that Yonkers is not going to work, in the same way that Belmont or Aqueduct won't work. And forget about Stamford as that's just completely unrealistic. Or perhaps Stamford could work, but that certainly won't be a New York team as nobody from the city will go to the games.