So, let's take this hypothetical (harrumph) youth. They see irrationality around them, obvious and immense, they see the waste and the pain it causes. They'd like to do something about it. How would you advise them to go about it?

Donate to CFAR. There's no good reason to demand a local increase in rationality.

[...]should we try to distance ourselves from atheism and anti-religiousness as such? Is this baggage too inconvenient, or is it too much a part of what we stand for?

We don't stand for atheism; we stand by atheism, prepared to walk away at any time should the proper evidence come about. (Of course, it won't.) In any case I think we should talk about atheism less because it is preaching to the choir and because the psychological principle of social proof makes people update on "a bunch of rationalists have all decided there's no god!" which is double-counting evidence.