Ya, that's probably your path, then. As you've probably guessed, realistic-looking skin is a definite challenge from a 3D rendering point of view. Part of the reason is that skin isn't opaque - there is a translucent aspect to it. Without factoring that in, renders tend to look, well, "plastic." iRay supports Sub-Surface Scattering (SSS), which creates this effect pretty well, but it's computationally intensive, which is why you need a GPU to get any kind of reasonable performance on it. That's not the only aspect to realistic-looking skin, but it's one of the big ones that has helped the G8 and later G3 characters look much more realistic than their predecessors.
Also, iRay tries (to the extent possible) to model light the way that light really works. This leads to more realistic-looking surface highlights, reflections, shadows, etc. But, again, lotsa number crunching. Earlier renderers couldn't afford this computationally, so they employed "tricks" to approximate the behavior of light, rather than trying to really model it. Sometimes extremely effective tricks, mind you, but there were always cases where the trick didn't really work well, because it wasn't the use case the trick was optimized for.
So, yes, if your goal is to be as realistic as possible, then you're going to have to invest in the hardware required.