A re-work of the resource importing is probably beneficial.
Issues:
1)Parts imported regardless of parts in stockpiles/manufacturing if importer is closer
2)Parts imported from closest importer regardless of queue quantity
A suggestion of prioritization:
1)Request part from closest stockpile
2)Request part from closest manufacturing
3)Request part from closest importer with empty queue
4)Request part from closest importer with queue of less than N items
5)Same as 4, but with greater values of N, perhaps steps of 5 or 10.
This way, if the part needed is available in the factory, it will not consume importer time or extra money. With steps 3-5, requesting from a lower queue will get the part to arrive much faster. I have had hundreds of parts in queue on one importer, and the importer 5 tiles over had no more than 2 in queue.