I think it'd be cool to be able to see something like "+50" or whatever pop up above an NPC's head after giving them a gift or talking to them and what not.
Doesn't even need to pop up above an NPC's head (because I think Friendship for talking is added at the end of the day, when the NPC isn't near you?) but it could be the same Toast notification you get at the bottom-left when collecting items or achievements