People have spent between ten and forty years saving for retirement. Will it be enough? Personally I really doubt people have saved enough with all the rising costs, especially with medical care. There are no government agencies keeping these costs in line. Year after year hospitals and doctors are allowed to charge whatever they see fit. Also, take into account the rising population in big cities and the landlord's ability to raise rent at their discretion. These two items alone will make it hard for people to have a decent life as our life expectancy lengthens.
Yes, the cost of increased human longevity will do a lot of damage to this country, and planet. The population as it is to high to be supported, and we will soon run out of natural resources if people begin to live a lot longer than they already do today.
Right now the cost of increased human longevity just means living healthier and recognizing medical issues when they arise. It does not mean anything crazy that will cause issues for others or be harmful on the planet. In the future it may be a problem but right now it doesn't mean much.
I do not believe the cost of increased human longevity is too great. Quite frankly, I do not believe you can associate a fair cost for this since increasing human longevity ultimately means that people are able to live, independently for longer. It doesn't simply mean they spend more time in a nursing home. Secondly, any cost associated with human longevity is created by people themselves. It has no consequence in reality.
I think that the cost of human longevity can be great, but it is up to the individual if they want to spend it. A lot of doctors will actually choose to not pay for expensive operations and treamens when faced with a life threatening disease and instead just worry about end of life. It's a personal decision.