Users that have retracted a close vote should be able to vote again on that same question.
I don't believe there is any danger in allowing this, provided some controls are in place (see below).
As a 3k+ user, I want to look at a question at any point in time and determine whether it belongs on this site and, if not, state exactly why it doesn't in a close vote.
People who write questions are free to edit them at any time. As a result, close votes can become invalid and the new close vote retraction feature was introduced as a response to this.
While I welcome the new feature, I wonder why we have stuck with the "you can only vote once" paradigm. If I'm monitoring a question to the extent that I withdraw my close vote, why shouldn't I be allowed to vote again if subsequent edits render the question unsuitable? I propose that if you retract your close vote on a question, you should be allowed to vote again.
Note that by implementing this feature, one would also be able to change a close vote (by retracting and then selecting a different close reason). To combat willy-nilly vote changing (which may confuse other users), I propose one of the following defences:
An edit must occur between retraction and re-voting. This ensures something has changed in order to make the user want to vote to close again.
A time limit ensures that X minutes must pass between retraction and re-voting.
No specific restrictions are enforced, but the reputation required to re-vote is raised to something higher than 3k. The idea being that more experienced close voters are unlikely to change close reasons lightly. Perhaps this could be a tantalising rep target at 7.5k (to fill the void between 5-10k).
A similar question was asked previously, but I'm hoping some of my defences listed above will negate the fears listed in the accepted answer.
Example Use Case #1
A poor question is raised and the OP receives several close votes and comments. Being a good user, the OP then adjusts the question to meet the quality standards of the site. One or more close-voters retract their vote now that the question is good enough.
But wait! A duplicate has now been found, which wasn't spotted originally due to the poor quality of the question. None of the retracting close-voters can vote to close as a duplicate and are forced to leave a comment. Hopefully passing 3K+ users will spot the comment and act accordingly, but unnecessary time is wasted. This question should be on the close queue and heading for death.
Example Use Case #2
Commonly on Stack Overflow, a user will present insufficient information to diagnose a problem. Perhaps their code example doesn't compile or they haven't provided definitions of all the referenced methods. I will leave a comment to indicate this and, after a small grace period, will vote to close with "This question appears to be off-topic because it lacks sufficient information to diagnose the problem.".
If the user edits their question and adds the info, I retract my close vote. But I often realise the question should be closed for another reason, e.g. a duplicate or the new(ish) reason: "This question was caused by a problem that can no longer be reproduced or a simple typographical error.".
Example Use Case #3
Perhaps the most common: you find a reasonable duplicate and vote to close. But then... you find the most wonderful, exact duplicate you could imagine. Too late, your vote is cast. You can retract it, but you can't then easily kick the ball rolling on a new closure with the real duplicate. Sure, a comment might cause things to start, but often it doesn't. Flagging for diamond attention isn't appropriate.
This can also happen when the OP refutes the original duplicate and provides some extra information that steers you towards a related but different duplicate.