Smoothing lofted surface (or different approach)

Hi,

I'm trying to make a manipulable surface from various interpolated curves. As shown on the attached photos, the 4 different curves share one point in the center of the surface.

The problem is that the lofted surface around that one point is not really smooth. I can understand why it's not smooth, since the 4 curves have different curvatures, but is there a way around this problem..? Maybe some command to smoothen out a lofted surface around this one point. 

An approach with parallel curves would probably be better, since the concave part wouldn't be fixed in the center of the shape. I did try to build the shape from parallel nurbs curves instead, but couldn't quite figure out how to "close" the ends of the shape properly. 

Any input on a different approach would be great.

Thank you.

Jens.