There is another way to make smooth curves when sculpting and that is to set your Stroke Method to Curve:

and add a new paint curve.
Then you can make a curve point with CTRL clicking and with CTRL click and drag you get a point with handles. You can adjust the Curve untill you are happy with it:

and then press enter to sculpt that curve with your selected Brush:

Especially handy when making repeating curved ornaments.