Your last suggestion seems to make things less democratic understandably, but how would it be implemented?Weighted votes based on karma. Or restrict the number of votes a user can cast based on karma or account age.
A problem with these kinds of things is determining what does or does not work and picking up on unintended side-effects, and doing so in a timely manner.
For example, if "young" accounts have very limited votes available will new users be less likely to stick around long enough to become more active voters? How long would it take to see this? What if by the time you recognize an undesired side effect you've already sent the site down the road of ruin (or something)?
For example, how long will pg keep comment vote hidden? How many people have found this to be sufficiently detrimental that they have, or soon will, leave HN and not come back?
How do you craft meaningful site experiments like this while keeping risk to a minimum?