Also, it's computationally difficult to compute 2-4 in real time (reddit used to do a similar calculation a long time ago, under the now defunct recommended section).
One other technique that springs to mind:
5) Set a minimum number of views or clicks a link must get before "falling off." So, if a ton of links are submitted around the same time, sprinkle them back into the mix -- perhaps using a version of Technique 1 -- until they've hit the minimum, then let them die a happy death.
If the goal is to draw in those who are most likely to make good founders and convince them to join ycombinator, then what you want is somewhere between echo chamber and reddit, but it is closer to echo chamber.