GREAT post, daigong. And thorough! I was thinking of putting a decent post together, but you did one ever better! If only someone would get the full Blu-Ray posted -- I want some nurse Risa. Sure, she's been a nurse a few times already, but each time it's a little different!
I'm solidly in the CVS camp, though in a narrow range: only Risa and Sayaka Ando really nailed my sweet spot. Some other popular models who are well out of the CVS range do tend to cool me down. Having listened a lot to Risa (radio shows and TV appearances, even though I don't know any Japanese), I think it's something she can modulate. The singing is definitely in her range, though there's obvious processing and probably tuning. Similar to her last single and the Enka cover (soooo hot!).
Thankfully, while she often does a higher pitched fun voice, I don't think Japanese idols do too much baby-talk, which I can't stand.