Thanks to agent008my, DeadSix17, handsomeboy1702 and Mikevhl for the helpful suggestions and info
I ended up trying a restore from CWM (backed-up first!) of my very first backup prior to any ROMs etc and just restoring the system only.
This seems to have worked a treat! As I now have the stock ROM and all my apps/sms'es/phone logs etc still in place before I did the system-only restore!
Exactly what I wanted and so easy!
Many thanks guys and huge thanks to the CWM peoples as that thing is amazing.