I've been hesitant to jump in here because much of what I feel has already been said, and very well. This is an important issue, though, so please forgive any redundancies. (Parts of this also apply to a few meta posts, including this.)
In addition to what J. Musser mentioned, there's a significant difference in some of the privileges once the site graduates. For instance, editing without needing review increases from 1k to 2k, and the ability to cast close and reopen votes leaps from 500 to 3k! Since some of us in the less than 3k group spend much of our time here just doing those tasks, the site will suffer more than we know if we graduate before finding a consistent system of moving people into a higher "tier."
So far, all of my "creative" ideas have been ruled out because SE doesn't allow much customization at individual sites. I'll keep thinking though, there must be something we can do!
In the meantime I'll add my two cents about voting, which is the backbone of entire SE system, and is a priority for me. I have Electorate, Civic Duty and other voting badges on 4 sites, am in the top group of voters even on graduated sites, and have held the top spot on GL in every category except "all" for a long time. Only recently have I really had to work for it, and I'm enjoying that! Thanks largely to these meta posts, and activity by users like Citizen, voting has increased, and the site has reaped the rewards! I hope it's not just a phase.
I've been doing a few things specifically targeted toward users who already have some rep, to try and push them into a higher tier. I recommend them to everyone.
- Pay extra attention to older posts.
- Check other sites for users we haven't seen in a while, and encourage them to come back.
- Welcome people who are already in the SE network but are new here.
Pay extra attention to older posts. Older posts are often forgotten, so make a concerted effort to look at those, especially if they have only a few, if any, votes. That may indicate a user who can't participate here because they don't have enough rep. Or, you might find an established user that's never gotten beyond a certain rep level and drifted away. When appropriate, edit the post, bringing it to the front page where a new group of users gets a chance to vote on it, and obviously to learn. (For your own reward, there are badges for editors. Also, if you're competitive like me, you can follow the stats on the editors tab of the user page.) Adding a new answer helps too. It brings the question forward, offers new information, and gains rep for you!
Check other sites for users we haven't seen in a while, and encourage them to come back. Especially on older posts, I check the rep of all users involved, including the people who asked, answered, and commented. I then look at their network profiles. In many cases, people with some rep, but haven't been here in years, are still active on other sites. Just in these last few weeks, I've found many users who've been long gone from here, but are right under our noses at a different site. Here are just two of many examples, based on data gathered 3/9/16: This user hasn't been seen here since October 2013, but was here 19 hours ago. This user, last seen here in 2013, was here two days ago.
Vote, edit, comment, or otherwise give them some attention, and watch to see if they respond. A "Welcome back" is just as important as the original welcome. If you see that someone has returned after having been gone a while, give them a vote and a welcoming comment. New rep for and from them can help close the gap.
Welcome people that aren't new to SE but haven't been to our site. They're often easy to spot. A poster with just over 100 rep is usually someone who already knows how to use SE, and has gotten an association bonus. Give them a vote and a custom tailored comment. Even if you can't answer their question, you can thank them for joining us. I'm getting good results from that.
I admit this kind of behavior can be tedious and time-consuming, however, if we're serious about closing our gap and growing our site, it's well worth it. New users are great, but we should make use of the untapped resources wandering around the network who already know and like us. I'm not saying everyone we "stalk" in this way will come back, but it's worth a try. I know, because it just happened to me! A year ago I posted a question on a different site. I got a good answer and then forgot about the site. Last week, I woke up to find not only rep, but a Nice Question badge, from that one post! The first thing I did was go back there.
A few final, though not necessarily original, thoughts about voting. Again I apologize for redundancies, and thank all of you who've already said these things!
Mods should be among the highest voters!
It sets a bad example for our community if the mods aren't voting.
Only one of our mods has even voted this year, and it's a low number. They're onsite frequently, and see most of the posts, so voting should be easy. I'm not minimizing the value of their other duties, I just think increased voting from them would make the site better, and help close the rep gap.
Vote even if you don't want rep.
Some of our highest rep people do the least voting, which shouldn't be the case. Not everyone cares about their own rep, but it's not about what we have, it's about what we give. If we don't keep that mindset, we'll never have enough higher level users to close the gap.
Empower new users. Don't forget that it takes 10 rep to post more than two pictures, 15 to upvote, 50 to comment and 125 to downvote. We welcome, teach and encourage new people, but we must use our votes to empower them. If they can't vote, they can't contribute to rep for others, and will not be able to help close the gap. We have only ourselves to blame if someone goes back to a lower quality site just because they didn't earn enough rep here to post some pictures!
Don't forget the people in the middle! Some mid or lower-level users have stopped getting votes; gone for a long time without seeing anything in the green "reward" box; feel a long way from the next privilege; and have begun to wonder if they're even needed here. Votes for them are essential to closing the gap.
Upvote questions you answer. We're blessed with an excellent group of people who answer a question, often within minutes of it appearing on the site. Sadly, some of the people who answer the most vote the least. That's one huge place where we're askew. In fact, I think it's one our worst problems, and is definitely not healthy for the site. Why answer a question that isn't worthy of your vote? Even if it has to wait for edits or clarification, at some point almost all answered questions should have votes from the people who answer them. Voting is private, so if you don't want it to be obvious that you're the voter, come back later and do it.
Vote for the post, not the topic. Even if you're not interested in the topic, that's not a reason to withhold the vote.
Upvote any question with a decent answer. If you like the answer, thank the person who asked the question. Remember, they need twice the votes to get the same rep as the person who answered.
Upvote subsequent answers. Many people are shy about adding an answer, especially if one has been accepted. Since it's human nature to read just the accepted, or most highly voted, answers, later ones are likely to have fewer votes. If you see that there is more than one answer, read all of them.
Finally, Make voting feel automatic. Consider resting your cursor on the arrow as you read a question. Then just click before you move on. Pretty soon, voting becomes automatic, and you have to remind yourself not to do it if a post doesn't warrant it. That way, voting becomes the norm, rather than the exception, and everybody wins!