I hit the limit of 25 close votes earlier today. Oddly enough, the Close Votes queue did not gray out, and I was allowed to "review" while not being able to vote to close.
This is inconsistent with the behavior of other queues. When a user is out of up/down votes, they are kept out of First Posts and Late Answers; those queues are grayed out on the main review screen. This makes sense: users unable to follow through on their judgement are not useful as reviewers.
Not so with Close Votes. When presented with this task, I could review it by clicking Leave Open (which I did as an experiment), but not by voting to close (which I would do normally).
Bug? I think so.