Thanks for the answer. It gives me some more insights.
I've just seen a post written by mutt cutts on "What should NO-INDEX do: Google no-index behavior. "
It answers some of my questions.
1. These pages are crawled and the content is kept.
2. Overall ranking? In a way.
3. No real answer.
However, based on what I learned - a bad url is a dead url.
You don't have a good chance to rank a bad url higher if it has started badly even if you improved it, no matter if it was indexed or not.
We are starting a site from scratch experimenting some things (that can't be done offline) and the question of no-indexing raised.