A few thoughts on this evaluation:
Quality on this site remains high.
There's a simple way to measure quality if you don't know a particular topic: if you don't understand what you are reading, it's probably of good quality. On questions that I have a passing understanding, the answers are clear and helpful. Some of the answers seem a little sparse, however. (Not knowing much about the topic, it's hard to tell how much more ought to be said in those cases.)
Voting seems low.
On the other hand, it surprising how few votes some of the detailed questions and answers are getting. I know the site is small and the number of users who are actively voting is smaller still. Since so many parts of the site are tied into reputation, votes are like currency on the site. It's difficult for a site to grow when people are stingy with their votes.
The core is small.
Having a core of dedicated users is important because these folks curate the site with edits, flags, and reviews. There are probably half a dozen people who make it a habit to participate on the site each week. We need more people to join that group.
More answers might help.
According to the Area 51 statistics, there are an average of 2.1 answers per question. But this sample showed only two questions with more than one. (One had 3 and the other 2 answers, so the ratio on these is 1.3.) Not every question needs to have multiple answers. But questions that have just one answer might be too basic for an expert site. Or answerers might not feel like additional answers are being rewarded (via voting) enough to take the time to provide an alternate or expanded response.
Google searches generally find this site.
On a smaller and more technical site, this is too be expected. The search terms I picked to look for the sample questions tended to be technical jargon. Most of the other hits were to online textbooks or encyclopedias where the terms were defined. It seemed unlikely that the answers to the specific questions could be found anywhere else on the internet.
Voting and user participation are closely tied. As they say in Chicago: Vote Early, Vote Often. Sometimes simply breaking the ice by upvoting an answer can give others courage (or at least a hint) to do the same. If you find a really great answer, you might leave a comment:
If you like this, please vote it up. It's important for the community!
Positive feedback from others on the site will encourage more of the same.
On the other hand, it sounds like some of the core users are getting bored (understandable after such a long beta) with the questions. Fixing this problem might also address the other two. The difficulty is for experienced users to find questions that other experienced users will find valuable. Renewing the weekly topic challenge might be a step in that direction. Posting questions and self-answering them when you learn something new is another useful strategy.
It can get discouraging to be in the doldrums of a long beta, but the good news is that it doesn't take much to get the community excited again.