Homebrew up-to-date, but do I need to worry about `could not link` + `delete path` errors?

All the specified files are just symlinks, so don't worry, just remove them.

To make sure that they are symlinks, you can run this:

file -h <what you want to inspect>

This worked for me:

../usr/local/..$rm -rf /usr/local/share/doc/homebrew

and then

../usr/local/..$brew upgrade