The answer depends on what you are selling. If you have a physical product that captures your target audiences imagination, your video does not have to do much selling. Take a look at the initial video for the Titanium Bike lock on KickStarter. The initial video was nothing more than a demonstration of a protoype bike lock. They added a number of videos once the product became a big hit. But much of the product's success was do to external publicity by on line web sites, that liked the product idea. That was handled by the bike lock inventor. So Kickstarter alone didn't make the product successful.
The new Pebble watch followed a similar path. Lots of external publicity and giant funding.