Good feedback, Larkin! Thanks for the input. We're definitely planning to introduce more themes for the Silverlight controls in the future, and based on feedback like this, we'll determine what skins are in the "highest demand." Personally, I agree with you that a "mimalist" design aethetic seems to be what's "in" these days on the web, so hopefully we can work on a theme that does that.
Of course, since the RadControls for Silverlight are truly "lookless," the sky is the limit. Anybody can change any aspect of the RadControls look-and-feel (quite easily in Blend), so that should help please all of the different tastes. Still, good defaults save time, and we'll work hard to deliver those soon!