I think treating karma like currency will only exacerbate the situation. I feel like the underlying problem is that the audience HN targets is a generally outspoken one - we have lots of opinions and little problem expressing them. That being said, what we say is not always accurate or worthwhile. So, the more people that are attracted to HN, the more comments there will be and thus, the more inaccurate/worthless comments there will be.
Most of the members of HN seem to have their own blogs, each with at least some readership. If it were just really insightful comments all the time, they would probably mention HN on their blogs, and word would get out. This isn't that hypothetical as that seems to be exactly how HN got where it is today. Anyhow, the growth will always be substantial, so the only way to keep it how it was would be to apply some sort of invite only membership or externally limit participation.
> what we say is not always accurate or worthwhile
Comments that are inaccurate or worthless can be voted down. An increasing number of low quality links has no real cost to the submitters but it has real cost to the quality of the site.
Right now there is nothing to stop the number of low quality submissions from continuing to grow. I don't think invites or membership is the answer. The challenge is to be open and high-quality.
How would treating karma like currency exacerbate the situation?
Most of the members of HN seem to have their own blogs, each with at least some readership. If it were just really insightful comments all the time, they would probably mention HN on their blogs, and word would get out. This isn't that hypothetical as that seems to be exactly how HN got where it is today. Anyhow, the growth will always be substantial, so the only way to keep it how it was would be to apply some sort of invite only membership or externally limit participation.