Hm. Strange that you can extend a Sketchup object, but not subclass it! One of the things which put me onto this path was a post (http://www.sketchucation.com/forums/scf/viewtopic.php?f=180&t=10299&p=69423) on best practice in coding for Sketchup, which recommends: "Don't arbitrarily extend SketchUp or Ruby base classes. Subclass them with your own class, and extend your class." Perhaps I am misunderstanding what this means?
Anyhow, what I'm trying to do is generate a bunch of objects automatically, based on user interaction with another object. The objects I'm generating would have a hierarchical structure -- just like a group hierarchy -- and would benefit from actually being groups which the user can modify at a later date. So, generally speaking, it would be ideal if they were groups. The reason I was wanting to subclass them is because they'll need a lot of associated metadata with various associated methods, and a subclass of a group would seem like an ideal way to accomplish that.
Is there a better way that I should be pursuing? Thanks for your help, by the way!