Great ideas. While we're at it, one thing I find a bit annoying is not being able to see at a glance the position of the player's country in another country's opinion diplomacy screen - IMHO, it would be better if it were differently color coded (e.g. white or blue) to make it stand out.Two additions I've long awaited but somehow forgot to ask for are a new message telling you that a vassal has been attacked and another one saying your vassal has cancelled the vassalisation (AFAIK there's only reminder for all vassals ATM).
Alternatively, it could be put always at the top of the list (and thus left red, yellow or green as it currently is) no matter if the player's nation is at +200 or -200 relations. Maybe this second option would be simpler.