That's the thing though, it's a paradox.
Anyone who is considerable enough to use "edit:" for legitimate reasons would not be the people who would be deceptive and change their posts to reflect a new opinion.
"edit: typo" is essentially just a defense against an imaginary accusation that you were being malicious.
By all means, edit posts to include extra information as an appendage, but closing with "edit: added info" is not very helpful.