You can restore 'suspend' by removing the file '/etc/polkit-1/localauthority/50-local.d/com.ubuntu.disable-suspend.pkla'. See How to disable suspend in 14.04? - Ask Ubuntu for further details. However you might experience problems (rhetorical question: why the file was there in the first place?).
Many thanks for your accurate suggestion, linuxium - thanks to which I've succeeded in restoring 'Suspend' to the session menu; but... (to be continued).
Turns out I didn't have permission to even look into '/etc/polkit-1/localauthority' - so I had to use 'sudo nautilus' in a terminal window to run the file manager as root, and that worked OK. Rather than just delete 'com.ubuntu.disable-suspend.pkla', I copied a backup to '~/Documents/Temp' for safe keeping, then quietened the original's efficacy by changing its name to 'com.ubuntu.disable-suspend.pkla.q' (ie: by adding '.q'). Sure enough, after a Logout / Login cycle, I could now see 'Suspend' to the session menu; however...
Here's what occurs when I choose the newly restored 'Suspend’ command from the session menu:
- screen goes blank,
- couple of seconds pause,
- screen comes back on again,
- pop-up alert: "Disconnected - you are now offline [wifi network name]", and finally
- pop-up alert: "Connected [wifi network name]".
Same thing happens when it's set to 'Suspend when inactive for 5 minutes' in the Power control panel. In short, looks very much like Ubuntu 14.04 cannot suspend the ICS.
Reading between the lines, it seems most likely that Intel just gave up on trying to get Ubuntu 14.04 to sleep the ICS in the way that Windows 8.1 obviously can - and so they used the 'com.ubuntu.disable-suspend.pkla' mechanism in '/etc/polkit-1/localauthority/50-local.d' to simply remove the 'Suspend' command from the session menu.
Frankly, I've found Ubuntu 14.04 on the ICS (onna quad-core Intel Atom Z3735F processor, July 2014 vintage, 1.33 GHz to 2.16 GHz) to be so utterly lacklustre compared to OS X 10.9 on my old MacBook Pro (onna dual-core Intel Core 2 Duo processor, January 2008 vintage, 2.5 GHz) that the Ubuntu ICS has been relegated to being an emergencies only contingency device - one which adds resilience, but isn't in day to day use. While the Ubuntu ICS can just about do one thing at a time, it is soooo woefully under-resourced in RAM and storage that it is a frustratingly slow and inept computer to use. So it's looking very much like I'll need to spring for a more competent and expensive contemporary Ubuntu PC (eg: System76 Meerkat » https://system76.com/desktops/meerkat ) to get a system that exceeds a 2008 MacBook Pro.