*(click for larger version...)*

CobaltDream, here's a shot of Princess' body using the same skin, same lighting, (even tho the lighting was only set up for her face,) same pose, etc. Granted it's not finished, let me know if you think it looks like plastic or wax.

Matching background plates is a completely different animal, and an art unto itself. In a way, that's why I do these skin-tests. Once I get the skin nailed-down in a controlled environment, I can put it in any scene, confident that I know that it will react to light correctly for the most part. Then it's just a matter of doing the lighting and maybe some slight tweaking. That way, if it's off, I know it's the lighting, not the skin, rather than chasing my tail. You tug something here, it pulls something over there, repeat, ad nauseum...
I feel it does help to be systematic about it. But, then, I'm anal-retentive, so that part of it comes naturally to me. 8op

All of the adjustments you mentioned, (variability of SSS around the neck, variation in tanning on arms, wrinkles on the elbow...) are all very valid details, and can be addressed fairly easily by customizing your own texture, bump, diffuse, and specularity maps, especially with nodes, and especially if you know what you're looking for and want, (which it sounds like you do).

And, no, I'm not one of `those guys'. I don't keep trade-secrets. I know how frustrating that can be, and I don't understand it. "I don't want anyone to be able to make renders as pretty as me!" That's ridiculous. That's not how I operate, or how I've been taught to operate. I go to 3D meetings every month with guys from Autodesk, Rhythm&Hues, you name it, where all we do is sit-around and share how stuff is achieved; our own as well as feature-film. Sorry. Off my soap-box.
Truth-be-told, I don't have any trade-secrets! All the stuff I'm doing seriously comes from just trial-&-error. Hell, I'll point you directly to the tutorial I used as a platform for these skin-tests - it's free on-line - but I hardly think it will answer all your questions. It's far from a "Make Skin Look Real" button. It's based on an alien, and my first render after going thru this tutorial looked like @$$.
I'm currently using mental ray. I didn't intially post in this topic to illustrate what skin could be achieved in Poser, specifically. I was just responding to the OP that the texture alone doesn't necessarily matter so much as what you're doing with it. I happen to be working with Victoria and the DAZ hi-res textures at the moment, so I decided to post to illustrate that point.
But please don't let that dissuade you: all of these principles are possible in Poser and D|S as well. I wish I had time to go do it in Poser and D|S, but I don't. I'm sorry. We've all seen it, tho. They're perfectly capable.

No, the lighting is not image-based, but I'm confident that the skin might look even better if I did use IBL, and I do plan on using IBL for the most part when I do start putting her in scenes. So if that's the case, why didn't I use IBL for the skin-tests? Wouldn't that make sense? No. Cuz, again, there's not enuf control with IBL.
All of these shots use 2 lights. 1 for general lighting, 1 `blown-out' light for hot-spot and translucency checking.
Remember that the "softness" that you're talking about can be a result of several different things, including the softness of the shadows, the quality of anti-aliasing, ambient-occlusion, and depth-of-field. (I'm not using the last 2 in mine yet, tho.) All of which can be adjusted in Poser. Keep in mind that SSS softens bump-maps as well. I'm sure the fast-scatter node is capable, but if it's easier for you to use pwSurface, (where, let's face it, as you mentioned, it's not a problem,) then do that.
I've also added a bit of reflectivity to her. No map. She's just reflecting the blue background right now. It can add a nice extra element, but you gotta be careful with it.

Take a look around. Find the people who are selling the products that sport realistic, no post-work renders, and purchase their product, especially the ones that include the lights and set-ups used in their renders. Take them apart, see what they did, and incorporate it into your own stuff.

I sure hope all this helps.