I had another thought about your model - well Sketchup generally - which is worth mentioning again.
Sketchup works better in large scale ie a factor of 100.
So an object you want to be 40x50mm would be drawn in Sketchup 4000x5000mm.
This won't help the smoothness of curves as the number of polygons is the same.
How it does help is when you are troubleshooting the model and zooming close up to vertices - I find that at real world scales Sketchup can't 'draw' tiny details close up, something to do with the way it handles Z-buffering I guess.
When your large scale model is complete, just group everything then scale by a factor of 0.01. It's pretty accurate, but don't rely on upscaling again to get the original model as some precision is lost in the calculations and faces/vertices tend to be ever so slightly 'out', enough to upset the inference engine anyway.
In essence, I always keep a large scale working model, with the 'real' scale model the one I submit to Shapeways.