Like I said, some people have turned it into more than it was meant to be (I had not seen the Sub D plugin, that's fairly new) because it's free, but that doesn't mean that is a workflow that anyone in this industry uses.
A few hobbies 3d guys doing some basic car designs using a smoothing plugin doesn't really make much sense other than being "king of the sketchup modelers".
If you want to do polygon or SubD modeling, Blender (https://www.blender.org/
) is a FAR more powerful tool and it's also free. But unlike sketchup it's a workflow that's properly designed for true polygon modeling, UV mapping, etc - and the skills learned there will much more easily transfer to Maya or 3D studio (which are still not ID tools - unless you only do 3D work for visualization or rapid prototyping).