ok, i was going to stay out of this, but this might be helpful.

"definitively not that "wow" effect anymore" compared to PR2 or from render 1 to render 2?  in the case of the former, i'd just say stick with PR2 then.  sure PR3 is more accurate, but bagginsbill is well into that 99% of effort to get the other 1% of quality.  PR2 is certainly enough for most. 

in the case of the latter, it's probably your lighting.  the shading on the first shows the extremes i'd expect of incorrect, linear output.  if i'm right, and in the first you aren't linearizing input and correcting output, so you have carefully made your lights work in an incorrect situation.  and you did a wonderful job of it, as many have. if you have a corrected material, you have to readjust your lights.  and if you, for instance, go from a light without proper falloff to one with, you really have to change them.  while hborre is saying your lights are too bright, what i'd say is they're not differential enough.  correction means you don't get yellow bloom, so when you want bright highlights, you need to really boost your lights for them.  and if you don't want everything lit uniformly, you have to concentrate your lights more, and use less ambient light.

if you want to know why to gamma correct in general, it's because right now you're not displaying what you want to display.  the renderer works linearly.  your monitor does not.  if you give the renderer non-linear input, then it's not working with what you think it is.  and if you don't correct the renderer's linear output for your monitor, you aren't seeing what the renderer actually means to show you.  it's like asking why to have a translator for two people speaking different languages to interact.

"So where's the easy to use User Interface for adjusting bump, specular, displacement, SSS, AO, where's the dialog saying not to ignore transparency maps or anything that is necessary for the skin to look ok?"  pardon, but how are you using transparency maps?  just asking because i can't think of a straightforward way to use transparency maps and skin, so i'm wondering if you aren't using them some other, more difficult to transform way.  i know i lost some connections when i applied VSS PR3 to a bought character.  unfortunately, i hadn't checked the shader to begin with, so i don't know what created the problems. but for some reason it used a duplicate of the diffuse map for a specular map and left the specular map hanging.  for me, the quickest way to deal with that was to delete the erroneous map and replace it with the correct node (took all of a few seconds), so i don't know if there's a more user friendly way to make a similar adjustment.  also, you should be able to use VSS to propagate the chages.

in terms of altering it, understand that while you can alter the skin fairly easily using the parameters, any of your customers would just have your presets.  Parmatic would give you the ability to do it in dials, but right there in the material room to the left of the Poser Surface node (rather than the right) are lots of parameters you can adjust to customize your specific use of the VSS PR3 shader.  my suggestion is to tweak things like SSS color and amount, tint, and shine.  but there's a whole bunch of things you control with that node set, and pretty easily for someone of your caliber with the material room.  yes, it's not a fancy slick interface, but really, is that necessary for someone who builds their materials from scratch?  and once you make it exactly like you want, it's your material to distribute as you please.

i hope that clears up some of the questions you had.