The quick (and probably flawed) solution I came up with was to have a tiered base amount that is determined by the karma percentile of the upvoter (eg, 75th percentile might get you an additional 2 points, 25-75 1 extra). Furthermore, there is an additional potential bonus based on the karma delta between voter and votee (ie, upvotes from top HN'ers are more valuable to newbs than to other top HN'ers). As an example, we'll say that we add one point for every 25% tier between the voter and votee (no bonus if they are the same). Using this example, a top-tier vote would be worth 5 points to a newb but 3 to a veteran.
This would allow high-quality posters with more recent accounts to quickly gain the necessary karma for voting, polls, etc without causing such massive karma inflation on the high end.