The market has moved a lot since Scion was launched... The Koreans have stolen Scion's "value" oriented customers away on the bottom end. The American companies have made huge strides in quality and refinement, while Scion has sat still. The interior of a new xB felt cheaper than my Subaru.
As far as "coolness," Scions appealed to the Fast & Furious crowd, which has largely grown up. The trend of "personalizing" and "modding" cheap cars on a grand scale is over. The only cars that get modded these days are enthusiast cars. I don't even see Civics getting fart cans and big wheels anymore.
Toyota should kill Scion and take its good/unique products back to the Toyota brand. Toyota can earn young customers again if they make cars that young people want. Not by "marketing" vanilla cars to them.