I find that my absurdity heuristic gives a strong signal against. Also, we can't be certain that it will work and we can't be certain how well it will work.

That's how the absurdity heuristic is supposed to work. But sometimes, it goes hilariously wrong, turning into an absurdity bias. You can't be certain, but you can make estimates.

This makes it very hard for me to evaluate as an investment. If I can't quantify the payoff or the odds, how can I justify the expense?

Every time you decide one way or the other, you make an implicit estimate. If you decide not to invest, you basically state that, given you current knowledge, you judge the investment as not worthwhile. This is not at all the same as "not being able to evaluate". You have to, every time you need to make a decision. What remains is to make sense of your decision, trying to not get it wrong.