According to my calculations there could not be less than 300 purple letters with no address and without the name of the sender.
Curses, or maybe they contain hope.
Without any meaning, those are people wishes and nothing more, moreover to be collected to this degree and the fact that they might not come to bee seen, I am sure there will be many regrets.
What does that bold sentence mean?
The fantraslation goes something like this:
Should they ever be brought to light they would produce many regrets.
ここまで蒐集されて=Be collected up to this degree
なお=In addition to that
人目につく=Come to light
事がなければ=This situation does not happen (conditional)
さぞ=I am sure
が生じるだろう=Will probably arise
Edit: 人目につく=Be visible, Be under public view.
If they are not visible, it will bring regrets.
Still it is differend from the fantranslation.