Actually, why should farmers be paid for when someone either stores or retrieves their data? I think they should be paid just for providing the resources, whether someone uses those resources or not. Of course the usage of resources should be measured by some system, so that network doesn’t buy something it doesn’t need. And maybe farming reward should be adjusted by the speed of vault, but I think there is no need to reward the vaults by their actual actions, only the need to reward them for being there for network to use.
Adding a bit:
We could have network wide price for storage space, that adjusts by the network need for space. Then we could have few categories that the vaults are ranked according to their speed. Faster vaults are paid more than slower ones. All the vaults at the same speed category are paid equal, regardless where the GETs actually come from.
The basic point being: every vault should be measured by their performance, but only rewarded by their potential, not by their actions.