I agree with your last, which is very unfortunate in that if we could figure a way via research to shift upward the effectiveness of cognition (for which IQ is a proxy measure), I think peoples lives overall would be improved.

Some of these are interventions that we’ve already found to prevent wasting of ability (as you cite in another comment); others might be nutritional or environmental changes we could make to better support development in utero or as children develop.

Giving everyone 5% “better brains” would be a huge win for the world, but the sociological factors you mention preclude widespread scientific study.