IBL does a fairly good job of faking ambient lighting - the way, in reality, things are lit not only by direct lights but by the light that bounces off other things. However, anytime you take aphoto you are using an even better approximation to ambient lighting ( :D ) and the results aren't always well lit, so having uberEnvironment doesn't guarantee good results - and it may not suit your image style at all.

HSS offers several options that the default DS skin shader (and especially the Skin lighting model in the default shader that is used if you don't set another) lacks - some can be used simply by setting vlaues, some need things like specular maps which you may or may not have with the sets you use (and which you will most likely have to set up for yourself). Again, it can add to your renders but it won't do so by simply applying it and hitting render, and it may not suit your style (though by the sound of it you do want realistic looking skin).

Before buying new shaders I'd advise grabbing the scripting SDK and using the upgrade lights script, which will give you new lights with slightly more controls than the defaults, and looking at the Default DS shaders in the DAZ free archive or the free shaders by Joe Le Gecko and Pendragon in the DAZ forums.