Most of the ground has been covered. Reduplication is a kind of phono-aesthetic phonological process that can be used for different morphological reasons: augmentation, diminuation, number (plurals), tense (perfects in PIE, Greek, and Latin), jocularity, melioration, pejoration, etc.

As for Pinker's explanation for razzle-dazzle, I say Pinker-shminker. There the stop comes first.

Ceci n'est pas un seing.