One Idea I've had for fixing this problem is to weight the value of a click based on position on the page. The further down on the page, the more weight its gets. Therefore the most popular topic at the top only get marginally incremented as people read it first and decide its worthy.
On the same note, if an article is waaaay down at the bottom, and someone's taken the time to read it and likes it, then it should get a good solid bump. This will create a "bubble effect" and allow those treasures that are buried deep down in the comment land, to rise to the top and even accelerate as more users find out and rank them.
This essentially is a formula to equalize the comments and give them a fair playing field as they battle for the top most position.
Glad to hear you like the idea. My method for reading through HN and others is to scan through items with a certain threshold. Once I get below the "fold" of the page, I start to lower the level so I can compensate for the "decay factor" you mention.
There's tons of good gems at the bottom of the page, and they need to compete at the same level as those at the top.
You could tweek the "weighting equation" and try linear, quadratic, or exponential type formulas.
You could also apply this technique to articles, so those at the top don't get overly hyped and those at the bottom have a fair chance to making some movement to the top.
Also, one thought in terms of the scoring value is to have it with a few digits of decimal precision. So you could still see how competing articles are doing at the very top and see your vote make a difference (be it very small).
On the same note, if an article is waaaay down at the bottom, and someone's taken the time to read it and likes it, then it should get a good solid bump. This will create a "bubble effect" and allow those treasures that are buried deep down in the comment land, to rise to the top and even accelerate as more users find out and rank them.
This essentially is a formula to equalize the comments and give them a fair playing field as they battle for the top most position.