That's why I like to read most of the comments on a post, because typically I'll find some useful information scattered throughout. After I'm done, I can roughly get a sense for "excellent comments", "comments that probably have a good point", "medium-quality arguing", and "probably just wrong comments". Then I may seek out other submissions of the same topics to get more data. Over time, I refine which points I think are probably valid. HN has its gems, just perhaps not as often or obvious as advertised.
I guess it's better to view HN as entertainment than expertise overall.