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I was always told that in order to get good surfaces, you have to start with good curves!
Do some curvature analysis on your 3D curves and make sure they are smooth. Then check your surfaces. Hopefully you imposed curvature continuity where the surfaces come together. Besides the surface analysis tool you asked about earlier, you can do a quick surface check with the rendering and lighting options, and looking at the "bright spots" as you rotate the model.
While the surfaces you built with GSD can have high quality with good surface continutities, I think the Freestyle workbench provides a higher level of surface modeling capabilities.
Both of the analysis in the attachment ("porcupine" analysis) show nice smooth transistion of curvature across the length of each curve. Both represent good, smooth curves. (My guess is these curves were made as splines passing through a minimum number of points?)
If the porcupine is very curvy or jagged, or has sudden changes, or crosses the base curve many times; these are signs that the curve is not so smooth. Any surface made from a 'bumpy' curve will inherit the same 'bumpiness.'
When is it smooth enough? That depends on your design requirements. A car body(that must look good) has a higher requirement than an airplane fuselage.
Try a "zebra strips" on your surface: View + Lighting and choose the Neon Light option. Any imperfections in the surface will show in the light reflections (the "zebra strips") as you rotate your design.