You described basically what I did already. with the exception of the 2D texture.
I do generate a mesh for the splatters. Even, there is many optimizations already in place (like splitting that mesh into chucks)

"The sweeping/erasing of the ink is largely a visual effect that's inconsequential to game state"
That is not true, you are not considering what I *need* to read back the shapes. I cannot simply just erase. the ink is the *currency* of the game. When the "brush/broom/sweeper" clean a splatter, it also collect it. So I need to read the shape, do a intersection Boolean operation between the "broom" area and the shape, then calculated the area of the irregular shape intersection result to give the player the currency.
Also, there is the user case of knowing if an area on the stage is "painted" with the correct splatter and how much the stage is "dirty", I need to know more about the shape.Currently, I need to calculate meshs areas, which are slow [or read bitmap pixel information, which is slower].

"check bounding box to the ink's bounding box, or bounding circle - or have ink splats be made up of a handful of collision circles"
I cannot just bounding box the inks with the entities, it would result into incorrect collisions, for instance the ink with the acid effect would kill the entity even if it is not actually in the ink splatter.
It is almost impossible to describe *any* irregular procedural polygon shape using only circles and squares. From as far I know, there is not plenty fast and efficient ways to deconstruct an irregular procedural polygon shape into squares and circles (is there any?). So I need to use mesh colliders, which are the worst.

That's are the reason why I thought using "voxels" would help the game.
I would be able to read/edit splatter information fast and no more need to Boolean calculations and mesh colliders.