I'm trying to guerrilla video record as many Wikimania sessions that I can attend, so I cannot respond at length.
But I do want to say: the cost/benefit analysis needs to consider the quality of the viewers and not just the quantity.
When a Wikipedian in Residence can show their institution the video of their Wikimania presentation as evidence of impact and engagement, it can lead to renewal of their positions and more initiatives.
When someone talks about Wiki Loves Earth, #100wikidays or other grassroots projects, video provides a unique window into the emotions and motivations you cannot capture in a mailing list or blog post.
When in 10 years, we want to know the passions and personalities that led us to where the movement is, where will we look?
If we're expecting Wikimania videos to rack up the same views as LOLcats, it ain't going to happen. It has always been a very small core community does a massive amount of the innovation and work that keeps the projects going, and the ability to talk to each other in deep, complex and accessible ways is vital.
For a movement dedicated to capturing the sum of all human knowledge, it's surprising how blasé we are in letting our own community history fall by the wayside.