There should be lots of champions, I think the problem with the current system is that right now they 1. don't do much, and 2. don't have enough out there to kill. Couple of ways to solve this problem.
First, have champions do more. That merchant out there, who nets you two gildars a turn if you hire him, should be trading between cities, carrying stocks of food, ore, weapons, ect in between cities and selling them for a profit. He should have his own money, and have the amount of goods and money he makes increase based on the number of trips that he makes. Everytime he comes into a city, the owner of that city gets a small sum (dependent upon the size of the city and the level of the trader) in tax revenue from what he sells. Initially he'll be alone and small time, but as the amount of money he has and makes increases, he should eventually hire guards to protect him and his merchandise. This is not a hired hero. This is him, acting on his own, out in the wild.
If you hire him, you should be able to do the same thing, the only difference is now you choose. Govern a city? That city gets a bonus to its income (which increases the more turns he spends as governor). Put him on a caravan route? He acts as a better caravan, and gradually improves at that. Or just have him in his nice safe market in your city? He nets you the two gildars (or however many he does based on his level) per turn that he does now. But that should be the least profitable of the options, since it is the safest. He should charge you a salary though, which increases the better he becomes at a given task.
That thinker, who nets you two research points if you hire him, should be able to increase research by a net percentage if he is governor. Or he should be able to manufacture special equipment, giving you better and unique items in your shops. Or you can put him in one of your libraries, and he churns out two research points. But once again, that should be the least profitable of the options. On his own he should be a freelance artificer, making items (better than what you can produce generically) and selling them to anyone with money. If he gets rich enough, he can create a little inventors cottage, which can be the source of quests and new equipment.
There needs to be lots of champions to see development like this, because for each freelance wealthy merchant, knowledgable sage, wealthy mercenary (at the head of a large army) or successful adventurer there are 10 more lying in a ditch somewhere.
Which leads me to point number 2. There needs to be more lairs and creatures, especially within your territory. These NPC's that are out doing their class job need something to do (in the case of adventurers), or some risk to them (in the case of traders and thinkers). There needs to be a dynamic here. If you are really good at keeping your nation and the area around your nation swept clean of threats, you should have a lot of traders and thinkers and administrators rolling around, because there are a minimum of creatures out there killing them. That being said, you will have fewer adventurers, simply because there isn't a lot of lairs to explore or creatures to kill. Mercenaries will go where the money is, so if you are at war or have a lot of problems with monsters, then you will probably see more mercenaries wandering around looking for employment.
Right now the problem with champions is that we don't have a "living world." They just kind of wander around not doing a whole lot until they get hired. Really, we shouldn't be able to hire most of the NPC's (wage costs are probably a good limitation here). Most of them should be going around doing their own thing, but continually influencing the world around them and your nation. Once they actually do that (if they do), then the problem should go away.