Q: A problem I have: Finding or creating an s-curve. One that will allow me to change both its height and width without slaughtering the smooth, symmetric curves of the shape -- no matter how wide I may decide to make it.
A: I'm not sure what kind of S-curve you need, but here's how I created one:
1. Use the Arc tool to draw half the S-curve.
2. Draw the second half.
3. Select both halves, and then press Ctrl+G to turn into a group.
Now you can select the curve, and use the grips to modify its size and aspect ratio.
A more sophisticated S-curve could be constructed using the ShapeSheet.