What in my opinion and experience, the most imporant ingredient is for a realistic render, next to VSS of course, is a good colortexturemap. In the last weeks that I've been experimenting with VSS I've tried several textures and only a few of them were good enough for me, even the new eltie Lana shader/textures didn't past my test. What important is, is that texture isn't too light, you need some contrast and changes of hue, otherwise the final result gets washed out completely.
Some texturemap are just a fill with a piece of skin and some cutout nipples, navel and pubic hair painted on (and sometimes not right on the spot so you get very weird results), but we all know that a real skin has different kinds of color, which differs with every person: sometimes a bit reddish on the elbows and knee, a whiter shade on the underside of your arm, legs, hands and feet, and some darker tones on the part that are more exposed to sunlight, sometimes a little blueish because of veins under the skin. These are things that VSS isn't capable off at the moment.
You can make those maps by using photographs and take pieces out of them, but it's also possible to paint a bodymap as long as you know where to put the right colors.
There is a big disadvantage on using photo's that I recently discovered: you can light a body as good as you can and take reference pictures for texturing, there will always be differences is dark and light parts, just caused by the shape of the body. I found this out when I realized that almost all my standing figures had a horizontal line on the belly with a darker color on the underside and a lighter color on the upperside. When I looked at the textures I noticed that a lot of them were lighther on places where the skin was on the upperside and darker where the skin was on the underside, especially the belly and the breasts, when you use this texture, and have some light from above (which in 90% of the scenes is the case) the light/dark effect is aggrevated, or you have to put your model upside down to compensate it.

Anyway: VSS alone isn't good enough (yet) for a realistic render, you also need a good colortexturemap.

Another thing I use against all advice is AO in the lighting. In my opinion is the AO in the shaders too weak (and strength doesn't work there), by adding more AO in the IBL I get more contrast. Be sure to switch off  smoothing in the rendersettings to avoid artifacts.

regards,

Bopper.

-How can you improve things when you don't make mistakes?