Comment 2 for bug 906952

The reduced performance in current trunk builds is not really related to paths created with the 'Spiro Splines' live path effect itself AFAICT - it is a known issue with already moderately complex _stroked_ paths:
Remove the stroke of the path in your example and add a fill instead (just for testing): new objects can now be added and edited as fast as in the stable 0.48 version, as well as node-editing the existing one.

See also:
<http://thread.gmane.org/gmane.comp.graphics.inkscape.devel/37154/focus=37156> (issue 2)
<http://thread.gmane.org/gmane.comp.graphics.inkscape.devel/37456>

Probably the same issue as reported in
Bug #844117 “Very slow when dealing with multiple objects”
<https://bugs.launchpad.net/inkscape/+bug/844117>
(unfortunately we never received feedback from the reporter of bug #844117).