As full support for Xubuntu 16.04 ends in April, I thought I'd try an upgrade to Xubuntu 18.04.  It went incredibly smoothly with a nice progress window giving information on what was happening.  In just under 40 minutes, including one reboot, the upgrade was done.  The only thing I noticed being not quite right was seeing two network icons on the top panel but that has fixed itself.  Xubuntu 18.04 includes a few new wallpapers but seems to be a conservative update which suits me just fine!

(From what I could work out the core Ubuntu components of 16.04 are supported until 2021 but the Xubuntu/XFCE parts are only supported for another 2 months.)