I believe there were several wi-fi calling packages, and at least some were overwriting a file that was not supposed to be overwritten, and this would impact data connectivity. I would have to track down the details, but hopefully this will help you along to find the resolution.I just wanted to follow up for anyone that may be kind enough to want to help me address this, or for anyone sharing the issue. I wiped cache etc and reloaded once more just to ensure it wasn't a fluke, and in the process of putting all my software back etc, I came to find out that the issue was caused by a Wifi-Calling for ICS package I was using from XDA.
Without the Wifi-Calling package loaded, everything works as expected from a connectivity perspective.
With the Wifi-Calling package loaded, I could always make make calls, but only had data if connected to wifi. Wifi calling was also working, because my regular cell connection was disabled.
I'm not sure if there is a better package to use with this rom, but I'd personally like to get my hands on it as it's a regular feature I use, and has been supported (typically out of the box) on every Virtuous ROM I've used - One of the biggest reasons I've been using them for so long!
Thanks for any input / feedback.