If another realm holds something secret it's impossible to use a
espionage action against it, since you don't know what to spy on.
Let's say that another realm are training some elite units (special
units with new abbilities) and hold it secret. Then you do not know that
the training excist and you can't spy on it.
But if you would have someone on you paylist in the military he would
inform you that such an action are taking place nad you will know what
to spy on.
Another good thing with this is that you don't need to use one espionage
action on every realm that are in you area. You will simply be informed
if there will happen anything of importance.
But this don't work always, since the man on you paylist may be in the
wrong area (a guilder would most truly not know about unittraining, but
an officer would).
The man/woman on you paylist would get payd 1 GB / information + 1 GB /
year or something like that.

//Finnsson

I like your idea! I do not know what the best way to do it would be.
:-(

What kind of limitations have you run into with espionage besides it
being too expensive?