As a modder, it would be hugely beneficial if we could actually determine the exact amount of spawns on a map, outside the current random placement. A problem right now is that if we introduce new resources on the map, they actually bump the old ones out.
You have the rarity tag right now, but I think a second tag would be useful, such as... <onespawnperland> or whatever. Then we could put a number in which it determined how often this new resource would spawn based on the number in that tag. You say there's one random spawn for every 150 tiles right now, so how about we have a similar functionality for the new tag where we can define one resource VS how many tiles are on the map. For example, <onespawnperland>350</onespawnperland> would mean that after the random resources were placed, it would ALSO place this resource once per every 350 tiles (obviously, 350 is a very very low number here).
Ideally, a resource could then have both the rarity tag and the new tag to provide some randomness.
My situation is that I want to create 5-6 new world resources based on a premise for a mod. However, the system as it is now is just way too random - I can end up with 6 of one type, 3 of another and 0 of the rest - even on a very small map. The new tag would solve that problem.
A third tag comes to mind, which would be something like <alwaysplaceatleast>, which would define how many resources would always be placed on a map, counting resources placed by rarity and the second, new tag. Let's say you get 2 from the rarity tag, then another 1 from the onespawnperland tag. If the alwaysplaceatleast tag was higher than 3, it would then place more until the number was fulfilled. This way, we could guarantee X amount of the new resource on a map, regardless of the size of the map. Then, rarity would take care of truly random placement for a unique experience, and onespawnperland would take care of modifying the spawn so that you always have a certain amount of spawns on large or huge maps, and alwaysplaceatleast would take care of making sure that there is always at the very least X resources on a very small map.