I think (following the cd incident) that retags, as a maintenance operation, should not bump the question to the front page. What do you think?
There's a proper way to do retags - make a proposal, wait for community consensus, create a list of questions that should be edited, and look at editing the questions gradually. I've done this a few times - for example, with respect to SAS, and i believe MC.
Editing old posts shouldn't be that common, IMO - the one case where it was necessary was when we had to fix image links.
I'd note that i've only seen someone get temporarily banned for overenthusiastic editing once, so its not a huge problem.