Let me tell you a little bit about what I try to do before retagging:
1. I look at the front page, especially the top 10-30 questions (since most people don't scroll so far down). If many of the questions in there are old already (either because I bumped them, or someone else did), I wait for another time to retag
2. I try not to retag more than 5 or 6 old questions at one time. (Though sometimes I lose track and do 7 or 8, but I try not to :)). That way, the front page isn't flooded
Of course, none of this applies to editing new questions, or other posts that are already bumped
I think from the votes on the answers to the meta question you asked, it seems like the community does care what the front page looks like.
That's what this is about - there are no hard rules on the official rate at which to retag. The idea is to look at the front page, and see how "stale" the content at the top is