The method I outlined does not require you to generate any stored data. Other than that foliage density map you wanted. I only suggested that you COULD generate unique foliage for each location using that method. You could simply choose one of four static meshes and not even rotate or scale them at all.
If you don't want a density map, you don't need to use it with that method. But then your foliage will be of uniform density everywhere. But it will be randomly placed, yet remain the same when you come back.
If you don't want to use a density map and you don't want it uniform everywhere, you could use some kind of equation, but why go to all that trouble finding one that looks okay? YOu could just procedurally generate a small perlin noise map and use that as your density map if you must and you can make a unique one for each level by storing a single random number seed.
If you don't want a density map, you don't need to use it with that method. But then your foliage will be of uniform density everywhere. But it will be randomly placed, yet remain the same when you come back.
If you don't want to use a density map and you don't want it uniform everywhere, you could use some kind of equation, but why go to all that trouble finding one that looks okay? YOu could just procedurally generate a small perlin noise map and use that as your density map if you must and you can make a unique one for each level by storing a single random number seed.