It would be nice if that were a dilemma that arose! Instead, at least around here, it's a question of preserving glades at the expense of shitty condos for rich people in the middle of working-class neighborhoods that've been established for decades and have no desire to be overshadowed - literally; the latest specimen is a collection of four-story buildings in a neighborhood of single-story houses - because some assholes with a taste for slumming decided to make a lifestyle out of it. And thank God for erosion! Because without it, there'd be "picturesque new luxury homes starting in the low 400s" right down to the banks of every river, stream, creek, and rivulet of drunken piss for five miles in every direction.
All animadversion aside, though, your suggestion of "a few hundred people [switching] from driving to walking commutes", merely upon the erection of a new highrise with good transit access, strikes me as idealistic unto sheer fantasy, at least in the context of current United States culture. I switched back to transit myself a year and a half ago, and remain very glad that I did - but it's not something that's happening on any kind of scale, nor does this situation seem likely to change soon. Getting to work via public transit and shanks' mare? That's something poor people do - poor people, a few goobers trying to make some kind of political point, and weirdos like me who grew up in nowheresville Mississippi and still sound like it after twenty years on the East Coast, and of whom it's therefore not surprising to see deviant, if harmless, behavior such as taking trains to work and following deer trails just to see where they go.
(Okay, maybe that wasn't quite all animadversion aside, and I fear I more hardly treat those whom I here sidewise describe than is quite properly their due - certainly they mean no harm, and had I not the experience that I do, I'm sure I would share the same sort of attitude I describe. But I'm having a hard time being evenhanded at the moment, because just last weekend I found one of my favorite verges had been torn up for shitty rich people condos to be defecated upon the place where it was, and this being baseball season, I'm getting a constant gutful of people slumming on my goddam trains. I suppose I should apologize for unburdening myself as I seem to have done, but what the hell? Perhaps it will elicit responses more worthwhile than the comment which inspired their origin.)