In my experience, spamming low-quality posts, not counting the bottom [-8,1] and top [30, inf] gets me an average of about +10 each. The trick is to keep posting comments small (readable at a glance), intriguing (just enough to warrant an upvote), and non-controversial points early on in a popular thread.

If you can't be one of the first commentators, it's best to reply in a way that puts your reply as close to the top as possible - replying to anything "below the fold" is a terrible investment.

[Aside: yes, I'm ashamed to care about karma enough to think these things through, but somehow, I just can't help it]

I think about these things too, but because I'm trying to prevent them from being necessary.

Unfortunately these are hard problems. I've been thinking about them since early Reddit and still don't have solutions.

And then you publically complain about being downvoted?

Only if I think it'll get me more upvotes ;)

Take a look at the top 50 and see their average submission and comment score.