A couple of MP UI things that I presume are on your list, but I've not seen mentioned:
1. There should be a way to decline a MP invitation.
2. Who goes 1st in a MP game should be randomized.
Controlling resources and denying your opponent access to them, while they are trying to do the same to you, is what makes it a strategy game. Problems arise when there is a certain strategy that cannot be countered. Then the game becomes a simple race to see who can be first to push the 'I win' button.