I don't agree that it is perfectly fine to use the moderator flags in matters of voting-to-close.
The Moderators would be the first to say that they are perfectly happy take a look at questions that need attention. That is admirable, but what you are requesting amounts to a supervote-by-proxy, and I don't feel that is appropriate.
Flagging should be reserved for egregious problems (blatant spam, illegal posts, profanity, etc). If you feel a questions should be close as off topic, that's what voting is for. If a questions doesn't get the votes, it shouldn't be closed. Otherwise, all you are saying is "my one vote should be enough." If Moderators have to act on these I-think-the-community-should-close-this flags, then the community is not doing their job.
I agree there are certainly scenarios where manual intervention may be warranted: Problems with a very old question fallen out of public view; illegal or personal issues where the community chose not to act appropriately; etc. In those cases, certainly, flag for moderator attention. Moderators are the "human exception" handler. But moderators should not be called to intervene in routine system community self-moderation unless it is absolutely necessary.
...I need to document what it is, exactly, we expect moderators to do. The short answer is, as little as possible!
