The insights in to the thought process of some of the smartest people around, and sharing of experience and knowledge, helps in overall intellectual growth. Hopefully, this would help in having a net positive impact in some ways in the respective spheres of influence of the people here.
As far as, jump in 'popularity' index goes for any idea/site that gets covered here, i would daresay HN hasn't yet reached digg/slashdot proportion. And it might never happen as well, given that the focus is to keep it targeted at a specific niche.
p.s. Standing and admiring oneself in the mirror for a long time is generally not advisable. :-)
There are a lot of times i see fellow HNers down-voting comments that are irrelevant and can hold themselves for not falling into the "stupid-war" like what usually happen in other discussion board.
That's the reason i'm here and not in Digg/Slashdot. The community are smart and critical.
However, most of that traffic is high quality, and provides insightful comments.
If I have to choose between a Slashdotting (100k+ visitors of extremely variable quality) and an HN'ing, I'll generally choose the latter - although being slashdotted is pretty good for your pagerank too.