Lets be careful with how we define pastiche. Pastiche in this context is always used in a negative tone, and almost always used falsely. A pastiche is a sound-alike or nod to a particular piece of music, it does not mean to write in a style. If one were to write a country and western "cowboy" song it would be in that style, it would not be a "pastiche". Whereas say, if one were providing music that *sounds like* a known popular piece that is unobtainable for copyright reasons, then that would be a pastiche.

If you are using pastiche just to refer to rock scores, pop scores and the like, then you are no better off when looking back with reverence at the golden age of musicals, as they were virtually all slow pop ballads.