Range extender and one module already installed and my feeling is that it might have helped at least a little but no statistic to prove that. (I remember that I saw some plugin/script someday that measured performance of z-wave network but cannot find it now.) Also during the winter time there seems to be more issues which seems to be caused by bad (radio) weather.
Funny that if I do regular status requests it seems to update luminosity sensor value but motion detection events gets slipped by.
I have the z-wave watcher plugin watching over motion detector part of the device so I can pass the data here if it helps?