Even more confused now as it suddenly works. 3.2.2.49 actually just downloaded and installed itsef while i was writing the previous message, so that might have fixed something at my end. Anyway, this is good news and will test it as soon as i get a chance.
EDIT: Can confirm that shadowplay/share works here in version 3.2.2.49 However i ran into a small problem and here's what fixed it for me:
During recording (in DIRT Rally and AC) everything seemed to work great at first, but watching the clips they had very noticeable black flickering. Tried different ingame resolutions, disabling the overlay and even disabling SLI completely. In the end the workaround was to disconnect all but my main display from the gfx card(s). I don't have a triple display setup as such - the two extra displays are just for other stuff - so i don't really mind disconnecting them when recording.