Modern rich humans live 80 or so years, but most of us have great difficulty planning (or following plans made for) more than a few years or maybe a decade out.

I don't think failure to think long-enough term is caused by our limited lifespans, so increased lifespan is probably not sufficient to improve it. In fact, the opposite is likely true: having longer views and considering multi-decade effects of today's action is likely to RESULT in longer lifespans.