having a Spline function smooth out the curve itself
Yep, the spline node could do that. You would input the data series points as control points, and the spline node would output a larger list of points that you could feed into Make Line Strip Mesh to draw a pretty curve.
Smoothing the data series points using linear interpolation
Actually that would be the hard part, because Vuo doesn’t yet have a node to smooth/interpolate from one data series to another. (Feature request: Smooth List Values.) I guess you could work out a solution using Build List or Process List — see @MartinusMagneson’s PetriDish composition.