Or put another way, we need to consider the classic story about the man who wished for eternal life but should also have remembered to wish for eternal youth.
Quality of life is all in the nerves. Avoiding dementia, Alzheimer's, paralysis, blindness, deafness, ... It's much harder.
http://en.wikipedia.org/wiki/Quality-adjusted_life_year
"Under certain methods, such as the EQ-5D, QALY can be negative number."
Does the government and private insurance stop paying for heart transplants and life-prolonging procedures after the age of 75?
I wonder what percentage of medicare/insurance payments goes towards prolonging life into the 80s and 90s?
I can't imagine being a doctor and having to make that decision, or break the news to a family that they're not allowed to save a life due to old age of the patient...
It doesn't matter who pays, the question still exists. Where to spend finite resources?
We're already seeing many advancements in earlier detection as well as reduction in symptoms for the issues you mention, if not improved prevention.
But watching someone spend 10 years with almost no quality of life while science slowly makes advances in those areas does not really help that particular family.
With the brain in particular... some kinds of damage cannot be fixed, no matter what advances we have in medicine, until there's a backup of the data available.