Why did it explode in such a dramatic fashion? I thought the booster was almost entirely empty when it returns to the barge.
If it hovered for 5 seconds at .5 meters, for example, could it burn off enough extra fuel?
The Falcon 9 cannot hover. The thrust of the single landing engine, even when throttled down to minimum, will provide significant lift to the empty rocket. That's part of what makes this maneuver so difficult and so awesome: it's called the hoverslam, where you achieve 0m altitude and 0m/s velocity at time = 0.
For reference, though, the Grasshopper/F9R-dev1, could hover due to it only having 3 engines, not 9, and because they could ballast it with additional fuel.
Also known as making a "suicide burn", at least in the KSP world.
Also, falling over almost certainly also leads to a writeoff, as otherwise they'd just fly the rocket into a big pit of fire retardant foam blocks.
I'd imagine that the lateral stresses involved in a crash landing are more than enough to write off the rest of the rocket, and so the explosion would just make the barge slightly harder to clean up.
They probably are spending more effort into not letting it fall over.