So I feel like there's definitely two perspectives:
1) permies folk happiness
and
2) traffic to permies happiness
In terms of point 1 - I think your videos fulfill all requirements and are just plain awesome. They help people find cool threads (and even make lotsa comments which inherently makes for a richer website) and it's refreshing and gets people pumped about
permaculture when things get stale etc. There is the potential that people could eventually get bored with it, but if you're always changing things up and what not, it probably wouldn't. Plus - people generally take in information a little better from a video than reading because that is the way of the internet.
Point 2 - Since this is more of the mission, it of course makes it more complicated. In talking to my smarty pants husband who's a marketer, (who actually found permies from seeing a PW video shared on FB) we discussed the things that usually make youtube videos work. Kind of seems to boil down to these things (which I think some have already been mentioned and most you probably know)
A) Title
B) Description
C) Tags
D)Time
Title, tags and Description are obvious ones, and having key words in there that people would want to find is an obvious one. Doesn't mean you're limited to stuff that is already out there, but titles, tags, descriptions etc seemingly should be clear and specific etc. the other thing (which is another you already know) is making it easy to get people to subscribe to the daily-ish mail and of course having the links back to permies (which you do already)
If all of those things are in place then it is possible it will just take time, especially since the SEO world has changed a bunch. So I feel like you could reduce the amount of videos you put out if you want to save yourself some time, and possibly change around what you put in them, like for example your tipi video got a staggering 11,000 views which by comparison some of your updates have only gotten 1000-3000. So, the specialized videos are definitely important as Jocelyn was mentioning. You could do like a big monthly roundup of permies awesomeness for the permies happiness and then try to brainstorm (maybe even in a different
thread?) of other videos that could be more specific that would get more views and shares etc to address the traffic to permies happiness.
My two cents