I'm happy to announce the biggest improvement since the creation of this mod. I've been working on a new spawn pattern, together with a major rewrite of the mapgen system. The latest code has a much more optimal and cheap architecture and results in a way better spawn pattern.
Previously, a radius was given and buildings would randomly choose a location within it, doing expensive checks to avoid other buildings. The new system arranges buildings into columns and rows, then jigsaws them into place under an uniform pattern. There are no more avoidance checks, and each building knows exactly where it goes before the system begins spawning anything. Buildings are now placed in line and as little space as possible is wasted between them, resulting dense and nice looking cities.
The new architecture also moves the hard work (position checks, trigger node search, terrain roughness checks) to a new function which simply returns the structure list and parameters. Spawning only begins after this list is received and we know where everything goes. Previously the dirty work was done per-building, resulting in laggy checks each time and resource intensive spawns. Performance improvement with the current architecture is visibly noticeable.
Here are some screenshots of how towns look with the new code:



Thanks to the better density, I was able to generate the largest town so far during one of the tests. Although it might seem scary when you think of all the nodes being spawned, it actually worked pretty quickly on my machine (single player). When the voxel manipulator will be ready, spawning of large and numerous structures will be a ton faster. This is the big town I got so far:

