My personal take on mercenaries is that they are very powerful. Have extra tanks for attacks is very useful, and I prefer to use them at the beginning of a tough battle, because I know they won't be coming home. They take the front of the initial attack, and soak up traps while the main army comes in from behind. I know that the mercenaries are expensive, but I am really seeing the difference between having them and not having them. And as I am playing at a lower gold league, I can easily find bases and five star them with my German war machine. This ends up leaving me with plenty of trade goods to use on them every once in awhile. Mercenaries also come off as an extra thing. They're not essential unless you are assuring yourself that you will get the five star, and even then you don't really have to have them. When it boils down to it, since mercenaries and blessings are so "extra" in the game, it doesn't seem so necessary to make them very very easy to obtain. Maybe a slight reduction would be nice, but I like the maxed out mercenary camp armies as an irregular occurrence that only comes when someone really wants to blow you up. Extra features don't necessarily have to be used if another extra feature is more prefered. We're lucky to have all these options in this little mobile game.
Campaigns also have trade goods available if they are being completed for the first time, but some players don't know that. Maybe show them along with the gold and food that can be gained from attacks.
I think dropping the required trade goods by 2 might help making mercenaries more available. This doesn't include diamonds. I would also like to throw in that having workers available makes getting trade goods infinitely easier due to resources found around the map. I would echo a suggestion made to have a blessing that gives you six hunters for 30 minutes that allow you hunt as if they were citizens. An alternative would be the hunters would automatically go out and collect all resources on the map, then the blessing ends. Apple trees, gold mines, and animals. (Obstacles maybe?) I would think that it should be cheap because if we need workers to hunt then obviously we might not have trade goods readily available, but then we might fall into the blessing replacing itself over and over again.
Take a stab at it. Looking forward to the future!