I suppose the best way to think about motion blurs is to think about the motion itself. Motion blurs are simply a way of making the animation flow smoothly between radically different frames- in Anime, it's referred to as 'ghosting', or turning into a ghost. Temporarily, of course. Ghosting what you call someone leaping from a roof in one frame, being their entire motion path in the second and having landed in the third. It tends to be comic booky- in fact, it is a comic book technique.

Think about comic books. You almost never see the 'moment of contact', except for in really vicious sword battles. What you see is the moment after- the raised fist and the reaction. What motion blurs- at least, in the 'one frame big motion' style- allow is for the artist to emulate this; it blanks the actual motion into a simpler form and allows the viewer's focus to be on the preparation and the reaction. For example, see dtek's falling pole, especially the second one. The second pole is ghosted almost perfectly- it goes from standing to about to fall to every falling frame in one go to having fallen.

Basically, motion blurs are useful for making the animation stay at nearly the same basic framerate while having radically different actual motion speeds. For your peices, the motion blur is useful in the sword combat one (sword moves smoothly) and the massive hammer one (hammer motion is more obvious), and the midair magic slash thing (natural magic trails). However, the falling-down-getting-back-up seems almost sluggish with all the blurs going on (they keep previous frames in the mind of the viewer), and they don't make the animation seem 'faster' or more 'actiony', except for the head-shaking spin lines. If you can animate it at the same framerate and it doesn't look sudden, then it doesn't need blurs. If you can add a single frame and it doesn't look as sudden, then it probably doesn't need blurs, though it might.