There seems to be one thing that is extremely hard to do per hand but can not be automated
Problem:
The thing is with island packing, if you want a good distance for the larger chunks, the small objects do eat a very disproportionate amount of space on the UV
> See image
As you can see on the image, or you may know, there are always a ton of tiny pieces, which are indeed small in your model and then proportionally small in the UV.
The island distance is good for the larger chunks but extremely inefficient for the small islands.
Improvement:
These small things could in basically all cases have factor 2 to 10x times the size and texture resolution with just using the existing space:
Manual improvement on some objects (extremely tedious and time consuming):
Suggestion:
Please add a curve for final island packing size + island distance based on original relative island size,
this could make UV packing far more efficient and make use of a ton of unused/wasted resolution for the smaller islands.