I agree that from a quality of life standpoint, and maybe an environmental standpoint*, living in a walkable area is better, but from an economic sense, it's entirely at a case by case basis because it's very easy to give back way more than your incremental per-mile costs in real estate costs.
I'm not finding this to be the case necessarily. I live in a studio in downtown Chicago with my husband. I've looked at homes in the suburbs, and no matter how I spin the numbers, my expenses will go up quite a bit if we move. For starters, in the suburbs near my office, 1 BR single family home (SFHs) simply don't exist, and 2 BR are pretty rare. Basements are ubiquitous. Of course, as the square footage increases, so does the price. Sure the price per square foot drops, but there is nothing of comparable price per month because "build big" is the norm out there. So already I've traded my walkability of 95 to a walkability of 17 and get to pay at least $600 more monthly rent/mortgage for the privilege.
But wait, there's more! Things that I don't pay for now that I'd have to pay for to be closer to my office: property tax, water, gas, electric, trash, sewage, and... other stuff (rented all my life, so I have no idea)? So that's like what? I don't even know how much that stuff costs in this area since I haven't had to pay for it since moving here.
Also, add in the expense and labor of landscaping, house maintenance, plumbing emergencies, flooded basements, snow shoveling, rodents, and bugs!
Oh and that walkability of 17 means we need a car (sorry, folks, I'll walk all day, but I'm not a biker--plus, they didn't even HAVE a bike score for this area), insurance, gas, tires, oil, maintenance.
Now if you have kids or you need a ton of space for whatever reason, go for it! But I don't think it's realistic to say it's less economical to live near city center, especially if you DON'T want 3 bedrooms, a basement, a 3 car garage, a workshop, and a backyard the size of an Olympic pool.
You did say case by case, which I would agree with to an extent. Other suburbs and places in the city limits but not near downtown probably do have 1 BR SFHs of a price comparable to mine--but aren't relevant to me because that's not where I work. But rent/mortgage being equal, homeownership would still be WAY more expensive because of all those other expenses. I really can't see how it would be economical to move even if my rent in my current place increased by $500+ per month.
That said, I DESPERATELY want dogs--you know how some childless 30-ish women go baby crazy? That's me right now, but with dogs. Some day in the next few years I might trade my nice cheap walkable lifestyle for all the joys of homeownership just so I can have those dogs. It's all about priorities.