Frogboy did mention it was a possibility at one stage to make cities immune from Tarth's Master Scouts effect (as he said, something like "It's really hard for cities to be stealthy").  So I don't think it would be a big change as of now for them to make it only work with military units and not cities or pioneers if there is enough strong support for it.

What do others think?

I would go one step further and remove the protection from units, too. Only the Sovereign and Champions should be protected.

You are absolutly not alone, that is pretty much an exact mirror of my sentiment. The problem is definetly in the implementation and the balance. The wooded terrain movement bonus alone is incredibly powerful in pure turn savings which essentially makes it an xp boost as well. Any and every turn based game has at its very core the idea that

1) There is a certain amount of turns it takes to a given games completion, obviously effected by map and other game settings

2) The ability of the player to reduce the number of turns and increase actions taken in a turn is as direct as possible a way to attain victory before the other players as is possible without introducing outlier game mechanics.

So how many of the positive traits center around a direct advantage in turn savings, One - Master Scouts. And its not just the wood movement bonus which in and of it self is worth 1 point as a faction advantage, the free moving settlers/scouts give you a direct turn savings for expansion as well as allowing you to have a larger city/resources engine which also translates directly to turn savings. So master Scouts gives you

1) Direct turn savings with Woodland movement bonus, which when combined with choosing all fights is effectively an xp bonus (youll be at level 10 on turn 25 non master scout player would be 10 or more turns behind, its definetly an "effective" xp bonus).

2) Higher surviveabilty for units by always being able to choose your fight, including free per unit unguarded trips back to cities to heal without fear of being killed on the way by a roaming monster, also can grab unguarded goodie huts with no risk. 

Example: So lets say your two initial heroes are traveling together and one gets really badly injured and its 5 turns of movement back to town and three more into the wild to take out that eay wilding warrior lair. If your sovereign went back and waitied for the healing with that unit (lets say the healing takes 3 to get acceptable health) your saving 5 for the trip back + 8 to get back to the wildling + 3 while your sov waits for his friend to heal so = 16 turns. Obviously you can do this with alot of risk without master scouts and the numbers aren't a perfect representation but the no-risk turn savings is very real and adds up fast.

3) Massive expanion bonus, pair it with wealthy and you will dwarf the AI in number of cities, with each one giving you a parrallel queue to increase asset (gildar/mana/etc) , we are talking 3 to 1 city ration player to ai and probably 4 to 1 with wealthy. Heck the tarth ai itself can pull off 2 to 1.

4)Ability to secure world resources, you can almost restrict the AI from getting anything at all, especially if you take an initially forward push deny strategy with completly no risk due to master scouts. Also gives you the ability to secure choke points and mold the map to your strategic goals.

I understand the lets make the factions asymmetrical and powerful and unique, I agree with that philosophy this however is not over-powered it's an "I win" trait. If multiplayer was available and it was competitive with no house rules you would be a moron not to take master scouts. Which by knowing this alone you ruin the asymmtry your aiming for because if everyone takes this skill why not just change the game mechanics to work this way and give people other more interesting risk/reward choices. Master Scouts is an all reward choice.

The only benefit I see is that it currently is a huge boost to the AI, Tarth can actually expand at the rate of the player without Master Scouts.

To leave it as powerful and unique I would change it by simply making it grant the stealthy trait to all units for free, anything that leaves in the 100% no risk of being attacked by world monsters is just too powerful as well as not being within the spirit of the game, to trek through a dangerous post apocalyptic world and be wary of the risk at all times.

Please don't post "well then don't play with that trait" or "mod it out" cause you can answer almost any critique of the game that way

Not much of a racial ability if the people of the race don't benefit from it. 

While I agree I don't like the stealth ability, I too much hate the free moves granted by the master scouts ability, am pretty tired of all the movement stacking in this game atm.

Sicnerely
~ Kongdej

I love the +3 attack and initiative bonus of the people of Tarth. Buth my hate for the masterscout abillity/trait far outshines it. I haven't and i shall never play with them, because of this abillity/trait. Buth then, I do play with insane monsters, so you know where my love is...

Monsters will attack cities that have master scouts in them. I've seen it (experienced it).

They just don't "see" the units when they're not in a city.  But when monsters go after a city, they target the city, not the units.

Master scout plays very differently than non-master scout.

Also it is the most powerful ability in the game.

I think having abilities that significantly change how you play is great, but there needs to be some sort of trade off so you choose it as a play style, you do not choose it because it is amazingly powerful.

Perhaps if it gave you a minus to research, production, attack damage, health, dodge, etc. Choose a few. It should also be split apart from move through forests and swamps. They don't have to be related.

Mike.

I've found that Monsters never attacked my cities when I was Pariden.  I think the Monster aggressiveness is probably lower in this patch.

I am thinking about making the master scout thing a blood ability and getting rid of the ill-fated attack bonus. Being invisible is fine, but I would balance that by only allowing them to get to level 3. So they have a ton of weak cities. Of course this is all mod logic, but it could be good balance for the core game as well.