I think it would be nice if most of the quest givers had some sort of actual lively animation that let you know they were fustrated, overworked, up to mischief, ect.

Then a option where you can turn off the quest symbol over the npcs heads, otherwise I fee like I am just looking at the symbol instead of the actual character I am getting the quest from.

Of course some npcs will be more subtle, like maybe an npc you see looking around squinty eyed for a suitable player to take on some task.

It could be it is just something that makes the npc more noticable, like some sort of slightly louder audio as you pass by them, causing you to stop by and talk to them and ask if there was anything that you could do for them. In particular those npcs would be the ones that are like, "Oh! Now that you mention it..."