Yes .. it's terribly hard to decide which folder to prompt with .. I used to prompt folder names by filetype (image etc.) and whether used to save or load. Over the years I've simplified that to separate save or load folders, and I think I'm about to go the final step and simply prompt with 'last used folder'.
No two applications seem to do it exactly the same way... :-)
So maybe your optional behaviour (rather than being for this specific import case) could be a "prompt with last used folder" for
all cases -- hence more widely useful. [In fact I just added that to my wishlist for MapGazer and PanGazer ... :-).]