Really, what you're asking here is "is paying for cryonic suspensions the most cost-effective known way of purchasing person-neutral QALYs in the entire world?" That's an extremely implausible position that almost no one defends. Even conditional on thinking cryonics was extraordinarily great, paying for research, e.g. scientific tests of the effectiveness of cryonic suspension and related biology, would be better. Thanks for saying that. I had the (incorrect) impression that there were many on LessWrong who did believe that.

future people might invent a perfect fire-suppression system, [...] But that wouldn't mean the early purchases were foolish Unless the post was edited, I don't think the OP was saying it was foolish; he was saying the payout of the decision was 0. Which is true, whether you're talking about fire insurance or cryogenics (unless there's a cancellation option in your contract). Now, there's utility in peace-of-mind which might make it small but not zero, but the point stands.