The 5D mark II is an amazing camera and it's value per price is only getting better as newer cameras come into the market. Buy it and install Magic Lantern on it (a free video app) and you will never look back.
Having said that, you make a keen observation that great videos (and photos) are a result of the creators and not so much the camera. I've seen great videos shot with cheaper cameras like the T2i. see Chalk Warfare 2.0.
However, if you have the budget to spare... a full frame camera like the 5DII will be more useful in more situations.
