I think this is a brilliant idea. If we could "crowd source" this evidence review, think of what could be turned up -- if only the assurance that it's not helpful (at least we would to have to wonder, and the video not showing anything could be a different kind of evidence in itself.)
I'm sure there are a lot of reasons not to allow non-LE people to look at things like this, but if you think about it like trying to save someone rather than save a possible future conviction, I think it puts the benefits into sharper relief.
Until she's found, I'm sure LE will make her being found a priority. The idea that a privacy of a bunch of party goers would even cross anyone's mind when some of these hundreds of people some may know more and yet that information can't be usefully accessed, it's just sad and frustrating. Somebody is not doing everything they can for the wrong reasons if every frame available from the Halloween and June is not being checked frame by frame. Time will tell who and why it is this way, but I don't think it is LE holding back.