So have you (or anyone, really) actually seen numbers crunched on the environmental impact of a more dispersed population? I haven't (which is why I ask), but it's another one those things -- I'm not 100% convinced (or even 50% convinced, for that matter) that spreading the population out is a good thing. There are efficiencies to high density urban areas that low density rural areas, well, lack. And vice versa. I don't know how the logistical considerations of maintaining our population through one means or the other stacks up against each other. But I am somewhat doubtful that it's substantially in the favor of going back to sustenance farming and suchlike. Once the population gets over a certain threshold, the game starts changing.
As for rustic life, m'own personal experiences have led me to largely conclude it's nice in small doses, but I wouldn't want to live it. Which is actually about the same response to city living. I like the in-between, where there's enough centralization there's actually shit to do (besides farm, drink, and fuck) and people to interact with besides bigoted fuckwits, but low enough density you've actually got undergrowth in places and the occasional bit of quiet. I'll give up meat before I give up theatre and easily accessed concert halls.