Mass transit is much cheaper to build and maintain as density increases. Assume every building has 4 vs. 40 stories, now consider how many homes / jobs / shops are within 0.2 miles of a subway stop. Further, how many subway stops you need to pass on the average trip. That's the real benefit to building up, walking simply becomes more effective.
I live walking distance from a metro station that recently was added in West LA, and it's been interesting to watch properties nearby being bought, improved, and turned over. Value around the station is being stimulated by the presence of the station itself. Increased density is going to follow it, not lead it.
I think this makes a lot of sense. If you start building your transport lines connected to areas that are already high vitality/value, then what you've effectively done is reduce the "distance" between every stop along the line and those key areas.
Let's not add commercial value, this is about solving real problems, not making money. The constant mixing of those two is what creates problems in the first place. There is no problem in having a an economical positive impact with a solution, but not solving a problem purely because it would "only" solve problems for many people instead of also making a ton of money is a bad way to live (at least, that's what it looks like).
You seem to have misunderstood my point. As density increases it is easier to build subway stations because the value measured in terms of money or units of abstract social benefit goes up proportionally to density.
That does not imply subway stations should not be built in low density areas, it is just an observation that as density increases subway stations are easier to build.
