1) maybe, depends on seat inventory
2) no way to know
3) if you were going to China, maybe. SFO-HNL, not worth it. The only difference you'd notice is a bigger seat, and a little more privacy. If you wanted to try it for 125 + miles, give it a try. But I certainly wouldn't pay a full cash upgrade.
Take a J seat upstairs on the 747. It feels like flying on a small private plane. For such a short flight, it's an excellent way to go.