I have helped organize and judge science fairs at my kids' school. I've moved on, and my younger son doesn't participate any more, because we do cool stuff instead. Built an arc light. Had a mythbusters-themed birthday party with liquid nitrogen fun and thermite. All the while learning how the stuff worked. We take apart things and try (emphasis on try) to put them back together.
In elemantary school, when little science is being taught in school, and the scientific method isn't at all, it ends up falling on the parent to emphasize the paper aspect of the science: a hypothesis, collecting data, recording data, control groups, etc., and if the parent isn't a scientist, or inclined that way, its just not going to go well. Frankly, at that age, important as process is to real science, it's terribly boring (and often it's boring at any age.)
I personally think that a maker faire with a long lead time and a strong effort to get parents involved with their kids would be much more meaningful to many of these kids, and likely incent the kids to further pursue these activities more than the science fair from our collective youths.