This subject has been discussed on Meta Stack Overflow, but many of the answers there are really only applicable to high-traffic sites, so maybe it's worth setting some guidelines here.
First of all, don't shy away from retagging, editing, or doing anything else to a question just because it's old. Old questions need love too. In fact, they probably need more of it, since they're not appearing at the top of the page for everybody who visits.
Next, make sure you've read the tagging guidelines. Actually, I think that question is getting a little long in the tooth and needs some revisions, but it's better than nothing.
Finally, some numbers. At present:
- We get 5-10 new questions per day.
- The oldest question on our front page is 3 days old.
- The front page shows 50 questions.
- On a high-res (1280px), maximized window, there are 10 titles visible without scrolling.
You should be able to infer some consequences from this with respect to the frequency of retags. In particular:
If you bump more than 10 questions at once, through retagging or editing, then you are pushing new questions out of the normal field of view (many people don't bother to scroll).
If you bump more than 20 questions at once, you are shortening the front-page lifetime of relatively-new questions by a full day.
If you bump more than 50 questions at once, you will have ended up pushing every recent question off the front page.
So please, retag/edit in moderation. We are still a small site, so do your edits in small quantities. If you plan to do a mass retagging, please notify us on meta first, and if what you really want is to rename a tag, then create a retag-request here on meta and one of the moderators can do it - instantly, without bumping any questions at all.
But other than that, go nuts. Definitely retag any new questions if you see any issues, and feel free to retag up to 5-10 older questions per day, as long as there aren't a bunch of other people doing the same thing. Also favour unanswered questions if you can; not that there's anything wrong with bumping an answered one, but unanswered questions will actually benefit from the extra attention.
Oh, and if you feel like doing some cleanup, just for the hell of it, I'd love to see the technique and cooking-techniques tags disappear completely over time; they're weeds from the 7-day private beta that sprouted roots and grew everywhere. preparation and ingredients aren't much better.
One final note: If you see duplicate tags on a question, it's likely the result of a tag merge. In particular, if you saw baking appear twice, it's probably because I merged baking-techniques with it and some people had both on their question.