Nikon EU are taking this issue more seriously than I thought, but having been away have not supplied latest lot of info requested...story continues.

Having had to do quite a lot of cache clearing and keeping an eye on the last few GB of HD memory left, I see that NX and View NX share the same cache, ie when emptying cache from NX prefs, it also wipes previews from View NX. Really just need a spare 20 or 30 GB on the hard-drive to keep them both happy