Very interesting stuff Purist and an excellent read.
I definitely agree with pretty much everything you've written, especially the problem with pinch corners.
I think Tilke in particular is guilty of this (who else
) - it appears to be that he uses a pen, a ruler for the straights, and a compass for the corners.
Seeing more sophisticated corners (decreasing or increasing radius) would be nice to see in his designs, rather than the almost digital-like characteristic of most of his tracks.
In my view, the best tracks out there are those with far smoother corners, and where it starts becoming difficult to differentiate between where one corner end and another starts - that's a good circuit IMO.
With Sketchup this is definitely a problem (great a tool though it is) - if you just use the curve tool once for each corner, you get lots of constant radius corners.