Yes, on a lot of fronts, but strokes, in particular, would be a lot easier to fix if the brain could renew itself. Fixing brain problems becomes much harder if the brain never regenerates.
> With 100 billion neurons we seem fine with what we have. The bigger question seems to be how to protect these 100 billion cells from degenerating.
Maybe. But we also know that those who age well seem to recruit cells from a different layer of the brain as they age. This would seem to indicate that the brain is having to "make do" for some reason which we do not understand.
In addition, what is "part of the brain"? Are the optic nerve or your olfactory nerve part of the brain? What about your spinal column? The computer scientist in me says "Of course" given how strongly linked they are with the processing.
Having a known ability to rebuild neural pathways would be important.
"The Brain That Changes Itself: Stories of Personal Triumph from the Frontiers of Brain Science"
https://www.amazon.com/Brain-That-Changes-Itself-Frontiers/d...
Prevention, as you mention, is a market.
Repair, is also a market.
Of course there are other factors.
That is a relative question. I imagine it really does matter to a variety of researchers in various fields. At the very least, it matters to those involved in so-called basic research.
We know that there is lots of redundant networks and plasticity, so if one cell goes down does it matter whether the gap gets filled by and old vs. new cell?
With 100 billion neurons we seem fine with what we have. The bigger question seems to be how to protect these 100 billion cells from degenerating.