I've seen a few questions around here about retracting close votes, and they bring up two primary points:
It's not obvious that opening the close menu again will allow you to retract a close vote you've already cast.
No one was ever told that the feature was implemented.
The request to allow close votes to be retracted was completed back in July of 2013. Since then, there's been no real mention of the feature at all. In all my searching outside of Meta, the only place the word "retract" even appears is in a Podcast blog from that month, which I imagine not a large portion of our user base even saw.
Worst part of it is, it's not even mentioned in the help center!
Just to be sure, I visited the cast close and reopen votes privilege page and searched for the word "retract" there too - still nothing.
So how are we to expect people to use this feature if we've never told them about it? Can the existence of this feature be made more well-known to users? I don't mean just making the UI more obvious, but making sure that documentation about it actually exists in the appropriate places.
I would go so far as to say adding a badge to advertise this feature may be useful. A simple bronze badge for retracting a close vote, possibly after the question has been edited, to teach users that the feature exists and how to use it. Retracting invalid close votes is definitely something we want to encourage, and we're very far from encouraging it right now.