I wonder whether #4 is the "exclamatory" sense of "rather", i.e. "more than I expected", or "slightly surprisingly":
1. I visited MrQ last week. Do you know, he's rather rich!
2. "How was your pizza?" "Rather tasty!"
3. "What's his new girlfriend like?" "Rather pretty, actually..."
(The intonation seems different from #2, as well.)
MrP