One of the key characteristics of research of the unknown is that you don't know the cost-effectiveness beforehand.

SENS (provisional on SENS still seeming like the best use of funds after more research was done).

What kind of research do you think could prove that claim?

The interesting thing of that claim is the idea that effective anti-aging research is research that's branded as anti-aging. I would guess that one of the most effective investments to further anti-aging research was the NHI decision to give out grants to DNA sequencing companies.

Investigating SENS more closely is also an interesting proposition. Doing so will show that it's over-optimistic and driven by assumptions that are likely wrong. However it scores high in the "clarity of vision" department that YCombinator uses to decide which startups to fund. SENS doesn't have to be right on it's core assumption to produce useful knowledge.

Startups don't profit from highly critical outside scrutiny into how they invest their money. Critical scrutiny might harm SENS.