So an earlier answer in the Blender meta site seemed to suggest that 1500 visitors per day was a desirable goal. If I read the stats for the Blender site correctly, were have more than 10,000 visitors per day, and we've apparently been in beta status since some time in 2013. What other hoops do we need to jump through here?
I do not think we are doing anything "wrong." SE sites can take a long time to graduate.
If you look at the stats of the other sites, we are in a good place. We actually place ahead of several full sites. The time in beta does not mean anything. The old 90 day limit has been done away with. Now the SE team looks at each beta site and lets it grow until it has a sufficient base of higher rep users.
If our nearly 2 years in beta has you worried, don't be. There are 55 beta sites that are older then us. Also, of the sites around the same age as us, our stats are much better.
Look through the different data points on the sites (and use the sort box) http://stackexchange.com/sites you will see we are in good shape.
However obsessing over the stats is discouraged, at nearly ever place site graduation is talked about.
So keep using the site, get more rep, and don't worry when that day comes. (I for one don't mind being in beta at all)