What lower hanging fruit are governments currently spending on? Giant militaries? Healthcare for those last few months of life?
I meant what lower hanging fruits governments ought to spend on. However, since you asked, here are some of the things governments are currently spending on, but could bear improvement: eradicating preventable diseases, ensuring kids get good nutrition, better tracking, and hopefully prevention of e. coli/salmonella outbreaks, funding basic research into improving outcomes for patients, reducing profiteering off the products of publicly-funded research, medical pricing transparency, better organ donor policies (universal opt-out)
We have a whole host of societal functions that are not geared to cope with longevity: including social security plus the associated tax-rates
We, like, know how to solve some of those other problems. Sure, there's politics and bureaucracy and complications and the opportunity for corruption, but you can assign a p close to 1 we could get it done in an arbitrary timeframe.
Meanwhile, what's the probability that dumping a particular amount of money into aging is going to pay off? Even taking a thousand years you need a p>0.002 to make it worth diverting money from the safe bet of getting a couple of years off the other things.
PS: Oh sorry I understood that as a question of what would be useful, not what is actually spent.