No, outputting them at all except when expressly requested will scare the living crap out of people afraid of computers. Wikitext is hardly wonderful in this regard, but error messages will make it much worse.
Not if the people writing to error messages keep in mind who they are for. "ERROR 574B: ''' not expected" will send most users running for the hills, sure, but "Please put ''' where you want the bold text to finish" should just help people learn. The best way to learn a new language (spoken, programming, markup, whatever) is by trial and error - that doesn't work if you can't identify errors.