okay, a bit of an update for anyone else using Solidworks and suffering these issues:
STL Scale
Firstly, there are no settings in Solidworks for adjusting the scale. It was set for Millimeters, but was being read by the Shapeways uploader as Meters.
The only solution was to save in STL, reopen in AccuTrans 3D, and on Saving (with options) setting the scale to 0.001 on all 3 axis.
NOTE: The suggestion to 'Extrude Pseudo 2D Surface' made my model seem quite screwed up in the thumbnail, but still uploaded and said it would print. However, it was saying it would cost 2x what it should, suggesting that it doubled the volume somehow.
STL Resolution/Quality
For some reason, there were errors in the app itself that meant that no matter how high i set the resolution detail, it would output at around 8K polygon.
It took me a while to realise that even though the preview showed a smooth mesh, it was still saying "is 8K polys ok?" when i saved.
I found that by starting at the "Fine" setting, i could nudge the sliders up a bit, exit the program, and the next time i tried to export to STL, it would be a slightly higher Poly count.
After a lot of nudging, exiting, opening, saving, exiting, nudging, exiting, opening... etc etc, i managed to get 10K, 20K, 50K, 100K and then finally 200K.
NOTE: I had to minimise the Part window when i was saving, as the preview of the mesh would crash the app - however the dialogue window would read out the number of triangles before you save.
100K looked okay, but there were still visible tessilation - only a slight nudge of the angle, doubled the Polycount and made it finally super smooth.
Final filesize was 10mb.
Up to 50K polys, the part becomes avalible on the website very quickly. I'm still waiting for the 200K model to become avalible.