A couple of thoughts I had in response to your situation.
I think the more directly you can demonstrate the value of your community with concrete examples, the more enticing it will be. One site I came across yesterday that does this really well is a medical practitioner community called SERMO. Unlike your site they have quite a few barriers to sign-up - all of their content is walled off for guests, and you need to go through a professional verification process to register. Despite this, what makes them effective at driving sign-up is that on their landing page they demonstrate the value and benefits of joining with real, specific examples.
I’m not sure if you’ll be able to read it because the site has text embedded in images, but for all of the things you can do (join conversations about the industry, start polls, discuss cases etc.) they give examples of actual topics and discussions pulled from the site. They’ve also got testimonials that highlight specific benefits. If I was a medical practitioner I’d definitely consider joining.
New communities are in a bit of a bind because you don’t initially have that track record to draw from. Unfortunately, this means that at the start when you make abstract claims like “Meet, Share, Discuss, Learn”, they’re just empty words. When people click through and see mostly vacant boards, those words seem vague and meaningless.
This is one of the reasons we recommend communities start small with a core group of users, and wait until they’ve achieved some momentum before they widely market their service. You’ve got one shot at that first impression - if you direct all of your Facebook, Twitter and email folk to an empty board right at the start, the sign-up rate will be very low.
Much better if you can get that core group of members interacting first, and from that you can curate for potential users some specific examples of your site’s benefits (or they can just click through and discover for themselves). It’s a great idea to use your existing networks to identify some leads who might be effective founding members, and work to get them on board. However, I’d hold off on any big announcements until you’ve got quite a few discussions going.
As to the video, think in terms of your purpose and target audience. I generally don’t like video and prefer text (I scan ahead as I’m reading and like jumping back and forth), but some kinds of content calls for it. Where I don’t like video, younger audiences tend to enjoy it and consume it much more. Likewise, perhaps there’s a core segment of your user that prefers video for accessibility? In other words, I wouldn’t just create video because you can - I’d only do it if I had a clear justification.