Please make a habit of using the [id://385430|your node] format rather than an HTML tag -- I log on to perlmonks.org, and your tag references perlmonks.net, which causes me to get logged out.

It's probably more efficient to /msg someone with the news of the update .. if you really want to. Otherwise, either they read it, or they don't read it.

If I think one of my replies was particularly useful I might go back (Hubris) and see what new replies or updates there are. I don't think I've ever bookmarked a node (Laziness) so I can go back and have another look at it. I'll get notified if someone replies to one of my nodes. That's enough -- I have enough other things to do (Impatience).

I sometimes use /msgs to notify someone of an update.

I think that having a node back in the Newest Nodes each time an update takes place, or at least with a mechanism like the one used for the home node, could be useful, so that significant updates won't be missed

Just my two cents...

If people get downvoted for posting a new reply to make sure the questioner gets alerted

Once again, you miss the point. You didn't get downvoted just because you posted a new reply, you got downvoted because your reply didn't add anything to the discussion. Simply posting a link to another site, without even a description of why, is both asinine and pointless.

then there should be an option to alert someone of a significant node update so he won't miss it

A "significant update" should almost always result in a new post. Adding a single off-site link is not significant.

Currently, the best way to handle a small but significant update is to both append the original post and create a new one, which is what I did. Appending the original will help people who've bookmarked it, and the new post will alert people who are just reading new replies.

I agree 100%, but again I reiterate that your example update was not significant. New posts containing actual significant information don't get downvoted, so your concerns are baseless.