Yes. Who are we to say what's worth keeping or discarding? Who knows what tidbit of information someone may glean from the info provided that may break down someone's brick wall.
For sites, I maintain, where the email address goes dead for the contributor - I mark the address as invalid but keep their query, or material submitted, so persons unknown to me may find clues. The only things I remove are on request of the submitter or where someone can show me the info presented is incorrect - and likely it will be a note alongside the original material.