Unless we have some particularly good reason to think that the unquantifiable ones (or some known subset) have better returns on average than the quantifiable ones, that's at best an argument for spending more resources on improving quantification.
This is beginning to sound like burden of proof tennis, I claim that most causes can not be currently quantified to any useful degree, therefore restricting yourself to the quantifiable ones is a mistake. This isn't a problem that can be brute forced - what will be the effect of say open borders? Or human genetic engineering? Or charter cities? Or a new Standard Model of Physics? Or Basic Income guarantees? No one has a damned clue, although many would like to pretend. This list goes on and on.
But even for the somewhat quantifiable causes, the long term e...
http://mentalfloss.com/article/54853/our-interview-jeopardy-champion-arthur-chu
I'm not sure I've ever seen such a compelling "rationality success story". There's so much that's right here.
The part that really grabs me about this is that there's no indication that his success has depended on "natural" skill or talent. And none of the strategies he's using are from novel research. He just studied the "literature" and took the results seriously. He didn't arbitrarily deviate from the known best practice based on aesthetics or intuition. And he kept a simple, single-minded focus on his goal. No lost purposes here --- just win as much money as possible, bank the winnings, and use it to self-insure. It's rationality-as-winning, plain and simple.