Okay so I talked to @o4kapuk a bit. I think I can understand the usage of OPERATE_SPAWN a bit more, although I feel like not many people actually use spawn capacity in this way.
Assuming traditional 6W1C3M miners, OPERATE_SPAWN makes very little sense. Actually, this is pretty much what was being discussed here. It seems pointless to increase spawn capacity for this. You run out of CPU long before you run out of spawn capacity for more small miners.
However, if you use spawn capacity to not necessarily make more remote mines, but to make bigger miners, it means that you are spending more spawn capacity on reducing the CPU you are spending per remote mine. I had already considered using large miners, but hadn't fully calculated the spawn load on doing it.
In this context the power makes sense. It saves CPU at the cost of energy and ops. I still think it is probably a bit underpowered, but It's closer to what I would expect from a power with this context in mind. I am not sure it fits with how I plan on using power creeps, but I can see where it could be used.
We'd need to stop developing and start debating on forums full time if we try to satisfy everyone's need for information.
K, that's a fair point