@focusstyle , dom , Disconnecting the ECT sensor will get the car to start almost 99% reliably, possible bad new sensor (iffy), or what this may mean is you should trace that circuit/wire for fault, short/break/corrosion/etc.. Just a thought, maybe try unplugging one injector at a time and try starting to see if a injector is grounding out ECU intermittently. Check the link below, may sound familiar to you. Sorry I could not help more but you have tried so much already. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
http://www.focusfanatics.com/forum/general-technical-chat/719513-2008-ford-focus-undetectable-intermittent-start-problem.html