For diplomacy I think it would be great if it was somewhat more realistic.
You don't think you can bother a nation's leader without any problems day and night, do you?
I would *LOVE* to see a kind of Chamberlain or King's Advisor role NPC, that 'picks up the phone' if it were, and that he then decides whether the leader wishes to speak to you.
You can try to bribe him/intimidate etc into letting you speak with the King, but that could work in your disadvantage.
If the position of the Leader is weak, he will want to speak to you immediately, with the ...(I don't know a good term...) Minister? welcoming you in and superpolitely telling you that the King is ready behind that door (or something).
If his position is strong the minister/advisor will just regard you as one of the lesser nobles at their court and tell you the King has other matters to attend to (should be quite a variety in these messages, dependant on the faction, the state of the diplomatic ties, etc etc). Of course the behaviour of King and minister should be different for each faction.
Regardless of the advisor (that you can bribe or offend and thus can have a personal problem with so you cannot have talks with the King regardless of your mutual like/dislike), you have once every 8? turns some kind of 'Open Court' and the King will speak to you immediately that turn.
The advisor should know how much you have spoken to the King and remember the results. If you just pressed 'offer peace', saw the cost, and exited a few times just to check, he may next time say "You're not sincere... how often more will you ask questions of the King without answering him yourself? No, you will not waste the King's time like that." and abort contact. He should also become even more angry if you then try it again that turn or the next two after.
Basically... diplomacy should feel like it matters what you do all the time (not too strict, we're not a diplomacy sim here). Makes it a LOT more realistic and fun in my book.
Also: I as a player can initiate diplomacy whenever I want, and they never seem to unless they're about to be crushed. This makes diplomacy feel unreal as well. I would wish for them to send you an ambassador or such asking you if their Faction Leader may speak with you. Begging if they're weak. Bribing just to speak if they fear you a lot. And that they ask for technology or such things.
I hope this will be considered, it would really be fantastic I think. Just explore the idea in your mind, don't go nitpicking details because that's not what matters yet.