I totally agree on this. You should have a working prototype to demonstrate its use.
Better yet, even have a manufacturer ready to start working on your product IF you get funded successfully. That being said, I also know campaigns that got funded even with 3D rendered images of their objects. So it is definitely do-able, if you have a nice, desirable sales pitch angle, and innovative idea.
In the end, it's all about marketing. That's what we're going to focus on from now. Even with an average product, you can have a nice video, awesome photos and make a good chunk of sales.
Browse kickstarter to get a clear idea of what others have done. Also, check the funded section