I can see that the multiple editing emails could become confusing. How about some sort of 'Re-post' button? That way, edited responses only get emailed out if the author feels that the changes are significant enough to warrant telling everyone all over again, and we can carry on subtly correcting typos and grammar without alerting all and sundry :)
Perhaps there also ought to be a editing time or post limit; it doesn't really make sense for people to be able to edit the first post of a subject after there have been 20 replies, or 12 months after it was written. Obviously FAQs and the like would have to be exempted from any limitations, but as these tend to be maintained by Admin level people, that shouldn't pose to much of a problem.