This is like saying computers should and can become faster. So X billion should be spent on future computers that maintain Moore's law, but none should be spent on anything that might exceed Moore's law.
Recent statistics on US health show reductions in overall annual deaths and that over 30 years the life expectancy has increased by about 4 years. Life expectancy background information is at wikipedia
If we look at the list of countries by life expectancy, we can see that there are already places that exceed the US life expectancy by 5-6 years Most developed countries continue to add 0.1 to 0.2 years of life expectancy each year.
Life expectancy has increased over human history at the same time that human wealth has increased.
Background on maximum life span
It is clear that living longer is good for people and for the economy.
It is clear that there is lot more that can be done to raise human life expectancy and life span. We should spend a lot more on pushing technological horizons outward in an aggressive way.
As part of a sensible portfolio of national scientific investment (medical, nanotechnology etc...), it makes sense that 1-10% should be on work with disruptive potential. In life extension, disruptive is an increase of 50% or getting annual increases to 1 year annually or more. That is 79 years expectency this year, next year 80 years, then 81 years etc...