As time goes on and users acquire more rep, we will see a jump in the number of users who have access to certain privileges. Being close to moderator tools access, I'm wondering if the amount of rep needed for certain privileges will increase. I'm curious if this has happened on other rep-based sites — if there are even other sites that do this type of thing — and what the pros/cons might be if the limits are increased.
No, I don't believe it will.
The rate at which the people with various privileges is growing should be proportional to the rate of new users in general.
So, as the site grows, the need for people with privileges will grow with it.
One thing that makes SO different than some other rep based sites, is that the amount a rep that a user can give is constant. (Excluding bounties).
For example at a site like DevShed when you agree with an answer you can give that answerer can get an amount up to 1% of rep. So as users get more rep they can give more for each agreement. This "inflationary rep" leads to new users gaining at much faster rates that old users did.
Contrasted to SO in which a user who has 5000 rep has basically put at much effort in as any other 5000 rep user, because each user who votes up grants 10 rep regardless of their level.