Your second point is one I hadn't considered. I suppose for some conditions, there would be a correlation between lowered quality of life and early death, in which case a 'longevity insurance' company would calculate quality of life as a correlated factor of longevity. For example, blindness probably has a higher rate of accidental death, so there would be some incentive for the insurance company to help, but the incentive is not as strong as the individual's desire for the improved quality of life that sight would bring.

As an aside, it seems to me that evolution has factored these correlations in as well. We have two eyes, presumably, because an insurance policy against blindness improves the chance of procreation. Unfortunately, as individuals, we don't necessarily want to maximize posterity, but some unique mix of longevity and posterity.