This is a terrible way to communicate your absence. It's spammy, potentially confusing and, worst of all, imitates a built in functionality of IRC. The _only_ correct way to set an away status is IRCs builtin `away` message.
You're advocating using a hacky workaround that stems from client-side UI issues, instead of using a well-defined built in message. This just seems wrong to me, in every way.
And I agree that nickchanges can be annoying; I guess I've never been in a channel big enough where it was a significant issue.
And yeah, it's hacky - but given that IRC is fairly bare-bones, I think it's a good human-readable compromise. You can register your afk nickname as well, and notifications work just as well if you configure your client/bouncer to highlight them both (which I think most do by default anyway.)
Two explanations are either yes, your client is configured to show active and away people the same; or other people aren't using the 'away' feature, so they show up as active 24/7. In the former case, fix your settings; in the latter case, it is other people who need encouragement to change - but encorage them to make use of the built-in away feature, don't encourage them to change their nicks :)