I started my 3D experience with 3DGS, and decided not to switch to Unity because my plan was that I make my WYSIWYG level editor(s) for my game (and other tools), and it seemed to be, and finally it was indeed relatively easy in 3DGS + Lite-C (and was the best way to learn this engine).

in Unity I would have needed more programming experience to make editor plugins. I don't really know how it works for WED, but in other engines I checked (Neoaxis, Esenthel, UDK) there are good/great possibilities to do it, e.g. by creating custom object classes.