Well, a month or so since I posted I've actually got a bit more first hand experience due to the usual "your PCP has x months left so come and buy another" call from the BMW dealer.
I've since had a sit in and a good prod around a Golf Style. Verdict? Perfectly fine to be honest - soft touch plastics in the right areas and the touch pads for example for raising and lowering the temperature on the climate control were literally 2 or 3 inches from your left hand when that hand is at 9 o'clock or so on the steering wheel. It was all a bit dull and grey and on the outside, other than the front, barely looked any different to a Mk 7, but all in all, it just felt like a Golf!!
I've also now driven an M135. Had a good 40 minute drive in that and I have to say that was a lovely car. Quick, sure footed and the interior was excellent. Miles ahead of the Golf. Yes there was £10k difference in price but if the GTi or R aren't any better inside they will be similar price and then you have a direct comparison.
I've seen nothing in my hunt for a replacement for the 330d yet. I think I'll keep it for the time being and have a look at the GTi when it comes out but I suspect I may stick with BMW now - the interiors on the latest models are superb.