IMO, they are useless.

I don't know how this bonus impacts the scouting (because, unlike haven def bonus, it's not explained in Help), but I cannot imagine a way to compute it in which it would be relevant against numbers used today. Plus, almost everyone "scouts" with Fireships today (send a FS, see what you've hit, estimate what's left).

I was told when I 1st started by a long term high up player, not to bother with crows nests, the only way not to be scouted is either scouting protection or full protection, or have that many dutchman up they win the scouting arms race.

As I got scouted by a Pirate Horde Player with 5555 scouts and 555 airships, the last one is not an option for me.

I think the question is " To defend your Heaven or Not to Defend you Heaven, only you can answer that question.

If you build dutchmen you use rum that war ships could be using, hench the catch 22, build the scouts, get the information but have nothing to deal with that information.

I think if you are defending a Bastion and or Presidios maybe some one should be alocated scout defence.