Now all working as I would expect
following your last comment about MASTER BROWSERS I attempted and failed to run the Lanscanner app you linked to on my Windows 8.1 Laptop. Digging out an old Windows XP Netbook to try, my NAS, PiNAS, was visible straight away in Windows explorers Network browser. This leads me to think that there may be an issue with Windows 8/8.1 and NETBIOS name resolution. Certainly there is a deal of talk about similar circumstances on various forums, often without resolution.
To make sure that I had NETBIOS running I followed this YouTube instruction
http://youtu.be/6l2O07MbaFg and enabled NETBIOS over TCP/IP. This may not be the final answer but it was a significant step on the way (see below)
Having got my Netbook working I ran the LanScanner on it and it did not show any Master Browser on my network (!) although it did show two devices in error, so it must have been one of those. These were Humax FreeSAT Satellite PVRs running a Busybox distribution. These are normally always on. Having powered them off, one of the other Windows PC's became the Master Browser and it all started working properly.
The earlier edit to the host file has now been removed
I have reverted the change to NETBIOS over TCP/IP I described above and it all still works, although I cannot say if making the change forced any other changes.
Thanks for your help, back to getting the NAS and DLNA Server working now
As an aside I note that you have commented elsewhere that the Logitech Server is not suitable for some of the devices, Do you think it would work ok on the RPi B+ ?
kevin