I'm a little curious - whats the need of your curves? Do you have a bunch of data (x,y) you want to convert to a spline? Spreadsheets can be a good help doing the initial data handling. Is your spline something you want to be used in CNC programming?
Is wing design your purposes? I found this http://www.designfoil.com It can export to several drawing formats, especially to the Excel format seems to be the way doing it.
I was operating a Makino MAG3 with a Fanuc steering making wings - and this use coordinate likely Excel coordinates.
My knowledge about wings is near to zero, but getting these data into a drawing could be nice. Having this we are quite close to make a CNC program making your wings in real. Manage this technology we also can making camshafts to engines, but this an other story.
Wing design is one of the function that I require to draw. More to the point, it is not the design, but the drawing of the plan view of them that I'm requiring. No problem with the airfoil section, as I import them from Profili2 as a DXF file.
I'll check out the links that you provide.