I'm late to the thread - just got pointed here from Slate Star Codex. I gave to Doctors Without Borders recently. Your analysis is pretty similar to mine except on two points. Douglas_Knight pretty well covered the first, about iteration. Supposing an infection prevention kit successfully averts an infection, we should not only count the expected half-a-life saved right away, but all the expected subsequent generations of infection that the averted case would have led to, until the end of the current epidemic.

Second, instead of assuming that a prevention kit goes to a random person in the entire population, I think it's more realistic to assume that it goes to the family member of a person who has either the flu, food poisoning, etc, or ebola.