Here's my controversial opinion that I didn't feel like posting in the more relevant thread: It is detrimental to society for old human minds to be preserved. History is lost with the elderly, but most science and technology fields move forward by bringing in new talent and ideas.
The obstacles of biological minds that are the reasons why old minds are so useless wouldn't exist though. The only reason why that happens anyways is some of several causes, all of which wouldn't exist if we go beyond flesh. Space: the human brain is roughly 4tb (forgot source, I'm sure a quick google will bring one up). As machines, that'd be completely upgradable, and not a problem. Really, the only viable second detriment is diseases like Schizophrenia. The human mind is naturally imperfect. If a HUMAN were immortal, they'd go mad. Get some terrible OCD, whatever. Living eternal life wouldn't drive a conscious robot mad. At this point though, the question isn't really "would this work?" but instead it's "Is this still us then? Are we still 'humans'?"
This is unrelated to my original point, but... A quick search found this, though it'd be disingenuous to say that neuron connections represent storage space. On one hand, there is plenty of space to store information within the biological contents of each neuron (Receptor count, exoskeleton structure, etc), all of which represent state information and affect each neuron's function. On the other, scientists still don't have much clue what information is redundant and what is essential. I'd take 4 terabytes with a grain of salt. The rest of your comment is just philosophy and speculations, neither of which I'm interested in discussing at this moment...Space: the human brain is roughly 4tb (forgot source, I'm sure a quick google will bring one up).
Huh, maybe I'm wrong. Nonetheless the human brain is imperfect in the way we don't have absolute control over it. You can't willingly think "Man, this right here is perfect. I want to remember this exact scene perfectly." We've almost got our own AI, that deletes what it thinks it doesn't need (as deemed by evolution) and remembers what it thinks is key to our survival and success in reproduction (as deemed by evolution). How cool would it be to truly access the full potential and functionality of every bit of our brain the way we can manipulate the root files of a computer? Again though, are we still 'us' if we can do that?
What you think of as an "old human mind" won't be preserved. After the singularity minds will have merged with technology and many (if not most) consciousness will be on a completely technological substrate. Minds will not develop in the same way as current biological human minds. Also, it is pointless to graph these future developments on how our current economy operates (i.e., the young replacing the old and bringing new ideas/talent, etc.). The economy will have dramatically changed as a result of these developments. What is important is understanding how it will change, and how we will individually be effected by these changes.