No, not all tildes, only those immediately following a space. These are the things that will make it impossible for people to write your URCs by hand, and it will be impossible to write a parser because as soon as you need lookahead, you are doomed.
All characters have to be possible to have everywhere.
Quoting have to be possible of all characters, and the quoting character have to always be quoted. No, they do not give the same information. They are different. It is too complicated because of the ugly syntax in the header value. I do not talk about IAFA templates.