What is the impact of a miner on the security of the network, conditioned on the event that it never successfully mines a block? I would think it would be 0.
The probability that a raspi ever mines a block (like, if it were to start now, not if it was going since the network first started) is negligible.
Therefore, I consider the probability that a given raspi would contribute to the security of the network, or, I suppose equivalently, the degree to which it contributes, to be negligible.
