The shine we try to mimic in 3D, which is essentially the oils, can be duplicated more effectively with the top coat. Strangely enough, I've found some great combonations with ethnic skin (some character's I've made promo images for are Cuban/Asian, etc.) and using a color for the top coat that one wouldn't think is even remotely like skin, gives great results. 

One fellow I have with caucasion skin uses a top coat in the area of 192 (light grey) in concert with some diffuse tweaks. Utilizing a self-made exr light file for IBL, I've gotten several renders where you'd swear its a photo. Same for an african american female, and an asian female. Lickably delicious ;-)  The asian has a top coat that looks like an orange crayon... 

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