So, I had a pretty good game going. I started with just Heaven until it was financially stable, laid out in a nice neat grid pattern (it didn't help, I still got complaints about roads eventually), then managed to get a nice Hell going with no problems popping up. And it went on like that until I'd expanded to literally every possible space in Heaven. Now it's constantly giving me lost souls because I literally can't build anymore of the rewards that they need, and they just plain refuse to develop the existing ones. I don't seem to have any problems with vibes or diversity, and I'm only about 1/3 of the way to the 1 billion souls goal... less, actually, since you need 1 billion for Heaven AND Hell. Hell isn't overflowing yet, but I'm running out of room down there quick too. What am I doing wrong?

EDIT: I think I figured it out, but am posting for others' benefit: Micro Managing doesn't work like I thought it did, and actually seems mostly pointless unless virtually all your residents are either permanent or temporary. I started over and began by messing with the planet's population to encourage them all to believe in the afterlife (to get as many as possible incoming SOULs), to believe that they go to either Heaven or Hell (to keep the SOULs from drifting all over), to NOT believe in reincarnation (which cuts down on the number who leave, increasing the permanent population and meaning I have to build fewer tram stations), and to believe in a single afterlife experience (again, to keep them mostly in one place... I think. I'm still not entirely sure how that all works).

Then I built only in Heaven (you'd think not building a Hell would result in lost SOULs, but there appears to be no drawback at all- I'll build Hell once Heaven is running perfectly, I guess), laying out different colored 3x3 squares in a grid of roads. And here's the part that seemed to make a big difference- I took it really slow, decade by decade at first, and individually balanced each building. Micromanaging them is time consuming, but appears to be the only reliable way to get them to evolve into bigger structures, which hold more SOULs and are more efficient, earning more money. I kept doing this as they evolved, eventually checking them once every 50 years instead of every 10, once they seemed fairly stable. This seems to be working extremely well so far- a couple thousand years into the game with a relatively tiny afterlife and my SOUL rate is already higher than when I had the entire map covered after 6000 years.

I still can't figure out what Heaven wants from me in terms of roads- my Heaven is basically an X shape with the gate at the center and short arms sticking out with the fate zones, and I STILL get the "Roads!" warning from Aria. I can't think of any way to make the distance shorter or more direct. At this point I'm just throwing up my hands and writing it off as some kind of bug in the game, because it pops up no matter what road layout I try. Hell's roads are easy- just make stuff really far away from the gate and it's happy. Luckily, Heaven having roads that are "a tangled mess" (despite being all straight, neat grids!) doesn't seem to actually negatively affect the game much.

Afterlife doesn't just measure the distance from the gate to the rewards, but also the distance in between the different rewards for the SUMAs. As heaven gets bigger, these distances inevitably grow. In short, there's basically nothing you can do to stop Aria from whining all over the subject. Thankfully, the only effect is that it delays spontaneous upgrades of the structures, but it doesn't seem to stop them from doing so eventually.