Today I was touring the mainland, by foot, by flight, and sometimes I just hop on one of those pods I've seen a few people complain about.
It occurred to me that, from a business perspective, the sheer ugliness of all that lumpy, empty land with the oversaturated ground textures would be enough reason to do something about the look of abandoned land.
So, I agree completely with @animats, and would add the further suggestion that abandoned land get some sort of (script deployed, perhaps) characteristic landscaping — with trees — so the world doesn't look like like a covered-over landfill. I recommend something specific to abandoned land, so people out hunting for mainland to acquire can tell the difference between abandoned land and the land of someone who likes to make gardens and forests. I realize there's probably a computational cost for landscaping, but I wonder if the cost of empty sim space that no one wants to buy isn't worse.
I've built up my land by buying abandoned land, and I specifically avoided areas that would put me next to vast hectares of other abandoned land, just because it's at least as unappealing as a tacky store or those giant privacy walls. Lightly landscaped abandoned land would be much nicer to live near.
(I did skim this entire thread, so I hope I'm not duplicating a suggestion.)