I'd rather they do some more than just re-spraying the external livery white and doing nothing to the interior. That is not refurbishment.
The business case does not stack up for Northern to put a new diesel order in to replace the 150s and 156s which are life expired or will be in the next few years.
The 769 Flex and 321 bi-mode Renatus project offer a potential imaginative solution that replaces life-expired diesel stock and increases capacity at a reduced price.
If all Northern trains interior were modern and clean like the 321 Renatus interior Arriva would see passenger numbers skyrocket across the North. They could get another 10-15 years out of the bi-mode 769s & 321s by which time passenger numbers would have increased sufficiently to enable a large rolling stock order come 2030.
Arriva need to think outside the box but should realise there is a potential solution that could result in a transformative change for the railways across the North if done right.
I'm afraid its a little late in the day to be arguing business cases for new Northern stock. The 195 & 331 classes will do far more for passenger numbers than cascaded stock, no matter how nice.