When I'm loading an image from a directory (very common for me), I spend time changing directories when I don't think I should have to. For example, if I load a movie poster, then a cover and then several person images, I have to change the directory for each image type because the file open dialog only saves the most recently used directory.
Having an MRU for each image type would make the image upload process easier.
I considered asking that PREFERENCES -> FOLDERS be used as a default, but I'd hate to overlap the intended function of the file paths (save external images to a folder, versus load images from a folder). This would actually work fine for me, but I don't have to provide support when things go wrong.