I think if done right, 'sparkle' characters can actually look very nice. If you can match the colours right it can turn out rather beautiful, I love the kind of creativity that goes into those characters.
While I am personally fond of matching together natural colours in a design, I am equally, if not more fond of adding in some simple unrealistic colours, as is evident with my OC Kiaz, and a few others such as Andreas and Zala. I personally love to add a lovely flash of bright colour.
I don't really have much care for the poorly thrown together 'sparkle' characters, I don't mind them being there, but I'm not overly fond of them. It's fine for people to make those characters, no one can stop them, but I don't pay them any mind.
But yeah, if done right, 'sparkle' characters can look equally amazing as any realistic design!