Pls read this post, too: http://forum.piriform.com/index.php?showtopic=23282
IMO, designing an intuitive UI is a challenge. Don't forget the sort and save entries in the context menue. Plus signs would not allow these. Have the view detailed results menu entry expand the node. I feel this could be a better solution, still allowing sort and save.
You could place a plus sign in front of each line to draw the user's attention the the sign, without the well known expand functionality. The context menu could open instead. -- This could probably be done better but I'm missing ideas at the moment.