The difference I see between the sparkle and the glass glitter is about which part of the drum sparkles, and how pronounced the actual sparkle that reaches your eye is. Picture a drum set on stage, and let us assume the audience member is 15-20 in front of the drum. If all of the lights in the venue are shut off except for one liko shining on the drum set, the silver sparkle will have a sheen that goes down the middle of the drum, with some various additional sparkles spread out about an inch in either direction from the sheen. With a broken glass finish, though, the flecks that sparkle are more spread out around the drum, they reflect a little bit more light (a tad brighter per sparkle), and the very definite sparkle sheen that goes down the middle of the drum is more broken up. I dunno how to describe it other than that. A glass glitter will look more like a starry sky with a high concentration of stars vertically oriented in the middle, and a sparkle will kinda resemble a light saber down the front of the drum, albeit with some additional sparklage just distal to the main sheen.
WMP seems a little "too" classy for a rock gig to me. Or, rather, the drummer is adding a touch of class to the overall vibe on stage. I like the look of a sparkle/broken glass finish a little better, though...