I think it makes sense to just remove that button and have theAgreed.
So, when quoting a message for reply, you want long lines wrapped?Not necessarily automatically. Sometimes wrap algorithms have unexpected results, which I'd like to be able to undo and re-do by hand.
Around what # of characters per line, 78?No need to push up against the standard's 80 limit, I'd go with more like 72, and then not count initial gt (">"), bar ("|") or space characters (maybe initial non-alphanumerics). That would avoid having multi-level quotes turn into gibberish.
FWIW, the emails currently generated with long quoted lines notIn the text/HTML, yes, but not so much in the text/plain part.
Speaking of which, maybe the format selector for a reply should match that of the replied message, saving the user's profile option for new posts. That is, my post was text/plain - your reply I think should be likewise, unless you deliberately change it. Or have I already missed that boat?
Too, I was thinking of the wrap feature in the context of a plain text reply. In HTML the handling of quoted matter is entirely different, and we need formatting tools to allow us to add and remove blockquote layers. I'm not sure if that's what the paragraph indent/outdent buttons do (they sure don't on Y! Groups).
Markdown likewise, since it sees paragraphs rather than lines, an initial > is to blockquote the paragraph is fine.