Check out how Milt Jackson uses dynamics and accents within his phrases.
Observe his mallets, how high and low the strokes are. Some strokes he lets the mallet rebound off the bars, while other strokes he "digs in" to mute the tone. Also vibes players sort ride up and down on the dampening/sustain pedal. It's hard to get all these subtitles to capture all these small details on the keyboard, but remember vibes are a keyboard instrument that are played with mallets instead of fingers!