I'd recommend you do neither.
If you set them to no-index, these issues won't matter, but you won't have lost the pages and whatever value they pose. Plus, it's generally good to keep any pages that aren't of their own accord, detrimental.
However, if you'd rather not do this, I'd look more favorably on removing them than fixing each one. That's a lot of work for very little reward - most likely, at least. Really, the answer depends on how much time you have and how fixing them would weight against the benefit(s) of doing other things.