a 2d elipse or circle like you said int he first post is a VERY different beast than a 3d shape. Please try to not leave out important details like that π
There are scripts that will subdivide 3d shapes like artisan or subdivideandsmooth. You could try those.
Subdivide - Free
http://www.smustard.com/script/Subdivide
Loop Subdivision - Free
http://www.guitar-list.com/download-software/sketchup-loop-subdivision-smooth-plugin
Subdivide and Smooth - $15
http://www.smustard.com/script/SubdivideAndSmooth
Artisan - $29 on sale right now
http://artisan4sketchup.com/
Though frankly, I'm not sure that subdivision will automagically make your model better. But it might be worth trying!
Chris