Imports cannot process new and updated records in the same file
It is not possible to make an import which makes new records and updates existing records at the same time; it would be much better if both types can be present in the same import file. When importing you have to either select the checkbox to update existing records using object IDs, or otherwise, you can only create new objects, and cannot update existing objects. This is annoyting when you have a file which contains some existing records combined with some new records.
Right now you get this error:
INVALID_OBJECT_ID '' is not a valid PRODUCT ID (details: Invalid object ID)
It would be better, when a blank object ID is input, if it would just create the object, instead of erroring out, and if a non-blank object ID is input, if it would just update the object. This would be a lot simpler and less annoying for users.