I've noticed that my allotment of close votes on SO no longer lasts as long as it used to. Maybe it's because there are so many more migration paths, maybe there are many more poor questions (more users means more questions and more questions means more poor questions), or maybe I'm just getting more curmudgeonly in my old age.
Regardless, it seems that reducing the domain of the site (fewer things are on-topic) should make more available close votes. And an increasing number of new users (most of whom ask poor questions or just dupes) would seem to indicate that a larger pool of close votes is needed. Lastly, as users gain more experience (either more rep or just hanging around for a longer duration), they also gain the knowledge of which questions have been asked before (better able to find dupes), indicating that they should have more close votes.
So my suggestion is that the number of available close votes increase based on one of:
- the number of close options (including migration paths -- 2 for each?)
- the number of users (distribute extra votes evenly among eligible voters)
- the rep of the voter (perhaps 1 vote per 1000 rep)