- Scout party. Similar to kidnappers/thieves, but slowly circle the fort, working their way inwards, scouting out traps, defense layout, army size, etc. If they were used in connection with the "Assault" and "Siege" attacks, it would be wise for dwarves to keep scouts roaming the land to prevent them from learning too much.
Don't really see the point, The only traps I keep outside are cage traps for the local wildlife, so what if the goblins know about those? Just less g's to hog my animal stockpile. If they get close enough to the fortress they'll probably get torn apart by whatever traps I have on my front porch or be foiled by the ol' locked door tactic, assuming they would get in, two words... war rhino...
To clarify I do like this idea, if it ever had a use, but without a reason to be worried about them why have them?
-- Add in "Assault" which is a larger force bent on outright destroying your fortress. Perhaps they can have better tactics, could include the planned digging forces, etc. I think having them utilize the scouts listed earlier to see traps would greatly increase the difficulty, you could not rely on just cage traps
Digging is planned, AI improvements are also planned. Such as if the siege turns right and they get chewed up by chainsaws they will go left next time.
I do like where this is going though and here are my ideas.
Stealing resources - Along with the hustlers there should be groups of gabbos that will come on your map, cut down trees, rip up plants and seeds in farms, mess up workshops so they can't be worked at, or nab your wildlife and pets. If discovered they will attack. They may walk on and off the map four or five times. While this really wouldn't hurt a self sustaining underground bunker fort. It would hurt you if you are doing an above ground castle or your in the middle of a golden plated pyramid. Desert environments where trees are rare would be effected the most by the cutting and plant gatherings.
Quick Raiding - Building on top of your raiding idea, I think a group of perfectly visible, unannounced mounted goblins showing up on your map and making a mad dash towards any dwarf would be extremely fun. When confronted with any military force twice as large as them they will flee.
Caravan Raiders - While most ambushes will make a straight line towards your fortress, this group of medium armored goblins will head towards the caravan as quickly as possible.
Wait Raiders - These raiders will wait outside, not taking a step into anything marked inside, they will target any dwarf/tamed animal that is outside the fortress. More educated and trickier then the regular goblin ambushes.