We went from a late T5.1 SE180dsg 4motion to a T6 Beach 150 manual. I'd be lying if I said that I didn't miss the dsg gearbox. That said the manual box on the T6 is excellent, (it was an ex demo vehicle otherwise it would have been another dsg).
The other big differences are that the former van was heavy, whilst the latter is much lighter, therefore the driving experiences differ. The SE always felt like a fully loaded van even when empty, whilst the Beach can be a little crashy over poor surfaces if lightly loaded. That goes away when the pay load is increased.
As for power, well the Cali is a leisure vehicle and I usually drive it in a leisurely manner. However both have good reserves of power when required and IMO, when the weight difference is factured into the equation there isn't much difference between these two models. Unless you are a budding rally driver, I also doubt if you'd notice that much difference in power between a SE 180 manual and a 150 dsg Ocean either.
In terms of refinement, I've read some comments that the T6 is more refined but personally I haven't noticed much difference. They are both quiet and refined.
Economy is another issue. However, in our case, a Euro 6 T6 150 manual Beach was always going to be more economical than a Euro 5 180 dsg 4motion by a country mile. However I think you will notice a marked improvement with your 150 dsg.
Apart from the above observations the difference between your old van and your proposed new van are minor. Some fancy new bling, a few more expensive options on offer, some but not all of the roof issues resolved, a few different but still dull colours to choose from and the same old iffy dealership network to support you. Despite all that, what ever California model you own you can be sure that you have the best car money can buy.