my favourites for hair are just about every Linday dforce capable (Side Layered Messy, Classic long, Bang Bob, Classic long curly). Using the G8 to G3 hair converter being able to use these with dforce on V7 s now is great

for textures Blue Jaunte has several Morph/Texture packages Sahel HD is probably the one Id really recommend. For pale skins the other texture makers who impress are Second Circle and Brahann.

I dont know the reason why creators do this but some skins you find out if you look at the value,red green and blue channels that the curves have basically been compressed into a thin band. Maybe iray is meant to work best with this part of the curve but they can look flat - the other possible reason might be that altering tone, curves or contrast quickly turns into a useless mess so people are less likely to modify the textures.

For darker skins Uchenna is good, or V7 Makeda by Samsil. There is also a renderosity product - a dark skin merchant resource for V7 that I often use that had subdermal, SSS, Epidermal, normal and bump channel textures but other than each texture beginning with DB I cant remember the name