How about simply making advisor's stats (and all characters for that matter) hidden? You could have interviews with applicants to try and determine their skill levels, but you could get it wrong, based on the skills of whoever was involved in the interview. There could be references from previous employers, as well as perhaps official university degrees (or whatever applied at the time) and just a general "reputation" that would be earned as advisors did their job.
This could make for clandestine offers to a rival's advisor, based on the reputation that he was earning from doing such a good job. The prestige of the relative rulers bidding for his or her services, along with their loyalty and ambitions could then be used to determine who they would like to work for.
Both during the interview and over time traits and vague levels of competency could be revealed to the ruler. This could be applied to family members as well, but of course with family members, stats and traits would be revealed far more easily as you know them much better.
Added to which, certain stats could be used to either conceal stats and traits - imagine the steward who while having a Midas Touch with stewardship, also is has the trait "embezzler" and while making great money for you, also siphons a percentage off for himself? Or the Charasmatic Negotiator who fools you into thinking that his skills as a Spy master are much better than they really are?
And also the loyalty of advisors could be effected by similar and opposing traits of the ruler. And thus why some advisors get fed up with working for their boss and move on. Sacking any advisor could give a loyalty hit to other advisors, unless they had formed a rivalry, moreso if they had formed a friendship.
Now, keeping track of all this for the AI would be a nightmare, so it would have to be something that was kept for the ruler whose court the advisor belonged to only. A simple one off random chance formula could be used for AI and only kept track of for the ruler of that advisor.
So, for an example, the steward to the Duke of Normandy dies and he starts looking for a replacement. Some advisors who are advisors to counts apply as they are looking for a better position in life. Some that are already advisors to Kings decline as they enjoy the prestige of living in a great court. And some in other realms who are simply disaffected with their current ruler or who only hold a court position decide to apply for a change in fortunes.
You get a list, and based off their prestige, perhaps the vaguest idea of their abilities and/or reputation. You can then interview the ones you'd think of hiring, and based on the skills of whoever you chose to help interview them, you'd get a further idea (which could be better or worse) of what they were like. You might get a list like:
Marshall: Poor
Steward: Very Good
Diplomacy: Average
Intrigue: Good
Traits: Honest, Modest
You then decide who to hire. Over the years you discover more and more about them, eventually getting a fairly good picture of who they are, depending on their stats/traits. You could build entire event sequences around the advisors and your interaction with them.
Now that would excite me. You get advisors and yet you're never entirely sure about exactly what abilities they have until you've known them for a while. By which point maybe they've ripped you off for years, or secretly seduced your wife, or murdered your children, making it look like normal deaths from childhood.
That's the start of an idea anyway, needs a bit of fleshing out. Would also make interactions with other courts interesting as you don't immediately know every single thing about your neighbour. Only what's known, based on how well known he is (prestige), the skills of his advisors and himself at influencing opinion of himself and the skills of your court. More interaction again gives more information. Thus making who you foster your child with more important.
The more I think about this, the more ideas I keep thinking of, lol.
