Top tip Steve - thank you! Will order from there, rather than ECP then as it'll come out much cheaper.
Though I'm now a little more less convinced it's the MAF. I took the car out this evening and prior to starting it up, pulled the MAF and it started at quite high revs (around 1200) and I could hear that same occasional pop / misfire once every couple of seconds. I reconnected the MAF and the revs came down a little but otherwise seemed the same.
I decided enough of nannying the car tonight and did take it for a bit of a thrash without really wringing it's neck and it drove great - the engine pulls extremely well at all revs.. low down and higher up, though I never really took it past 5000RPM. Sounded lovely on song too - had forgotten just how good the VR6 sounds.
There's definitely something not 100% and sure it's electrical rather than anything more sinister. It's just this noticeable, very slight misfire at idle, and also I find at lower revs and part throttle when driving at say 30MPH it feels a bit like.. not comfortable.. very slightly hesitant and a touch jumpy.. like it wants you to either be on the throttle or off the throttle and part throttle seems difficult for the car somehow?
And lastly.. idle.. seems to take a LONG time to settle down to the lower VR6 idle speed of 650RPM.. it won't do it until the car is fully warmed up, and instead runs on a faster idle. And then when it has settled down to the correct idle, despite the revs being locked solid where they should be there's quite a lot of vibration into the cabin - like it 'feels' like the engine is misfiring a bit and you can feel it kicking through into the cabin.
Will be interesting to stick the loan coil pack on and see if that improves how it feels. It does have this vague whiff of coil pack about it.
Sorry for rambling on - just now having done the engine work, I'm on a bit of a crusade (or should that be folly!!) to sort out all the gremlins on the old girl and get her ship shape :)